l1li

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GOVERNMENT OF KENYA

MINISTRY OF NATURAL RESOURCESGEOLOGICAL SURVEY OF KENYA

GEOLOGYOF THE

END AU AREA

EXPLANATION OFDEGREE SHEET 53, N.E. QUARTER

(with coloured map)by

B. H. BAKER, B.Sc., F.G.S.Geologist

Seven Shillings - 1963

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Report No. 62

J'-

l1li

-- -~- -

GOVERNMENT OF KENYA

MINISTRY OF NATURAL RESOURCESGEOLOGICAL SURVEY OF KENYA

GEOLOGYOF THE

END AU AREA

EXPLANATION OFDEGREE SHEET 53, N.E. QUARTER

(with coloured map)by

B. H. BAKER, B.Sc., F.G.S.Geologist

Seven Shillings - 1963

- -.. ~.-- - m

Report No. 62

J'-

Report No. 62

MINISTRY OF NATURAL RESOURCESGEOLOGICAL SL‘RVEY OF KENYA

GEOLOGYOF THE

ENDAU AREA

EXPLANATION OFDEGREE SHEET 53.. NE. QUARTER

(with csluured map)

byB. H. BAKER. 8.512., F.(}.S.

Geologist

Seven Shillings - 1963

FOREWORD

The Endau area consists largely of an almost featureless plain, from which almost nogeological information can be gathered by ordinary surface methods. From the plain,however, there stand up a few hills, of which the most important is Endau. They are re-markable in this part of Kenya in so far as they consist of intrusive rocks of syenitic andallied nature, including alkaline types. Around the syenites there are well-developed zonesof fenites. The nearest known relatives of the syenites that occur in masses of notable sizeare found at the centre of Mt. Kenya and at Jombo in the south-east corner of the Colony.Such intrusions are frequently associated with carbonatites, but no carbonatite was discoveredin the Endau area. It is probable that, if they are associated with carbonatites, the carbonaterocks have still not been exposed by erosion.

The mapping of the area did not reveal mineral deposits of any commercial interest.As in many parts of eastern Kenya the most important mineral in the area is water, and thereport gives an account of what has been done in attempts to improve the supply.

Nairobi,15th February, 1960.

WILLIAM PULFREY,Commissioner (Mines and Geology).

~

FOREWORD

The Endau area consists largely of an almost featureless plain, from which almost nogeological information can be gathered by ordinary surface methods. From the plain,however, there stand up a few hills, of which the most important is Endau. They are re-markable in this part of Kenya in so far as they consist of intrusive rocks of syenitic andallied nature, including alkaline types. Around the syenites there are well-developed zonesof fenites. The nearest known relatives of the syenites that occur in masses of notable sizeare found at the centre of Mt. Kenya and at Jombo in the south-east corner of the Colony.Such intrusions are frequently associated with carbonatites, but no carbonatite was discoveredin the Endau area. It is probable that, if they are associated with carbonatites, the carbonaterocks have still not been exposed by erosion.

The mapping of the area did not reveal mineral deposits of any commercial interest.As in many parts of eastern Kenya the most important mineral in the area is water, and thereport gives an account of what has been done in attempts to improve the supply.

Nairobi,15th February, 1960.

WILLIAM PULFREY,Commissioner (Mines and Geology).

~

FOREWORD

The Fntlatt :trett consists lead; at ttn ttlnmst featureless plain. l‘mm which almost nogeological internuttittn ettn be game-red h} m'tlinztry sttrt‘ttee methods. From the plain,however. there stand up L1 few hills. 01‘ which the must important is Ettdtttt. they tire re-markable in this ntrt of KNUKE in so tltr as they emtsist ut‘ intrt ‘ e roexs 0f syenitic andallied n;tture. including ttlkttline types. Armtntl the syenites there are “Cli-JCVClODCLl mitesof fenites. The nearest known relatives at the genites that occur in masses of nuttthle sireare found at the centre til Mt. Kenya and at .lornho in the smith-east corner at the Colony.Sueh intrusions U. re frequently asst eleilCLl with enrbctntttites. but no ettrhuntitite wits tlisem eredin the Enduu area. It is g‘l‘ObllJlC thctt. il‘ the} tire :t'ssoeirttet'l with ettrlmnatiies. the carbonaterocks have still not been e\posetl by erosion.

The nt.tppi:tg of the atrett did not re\e:tl mineral deposits of an} commercial interest.AS in many ptirts of eastern Kenya the most tntpm‘tttnt mineral in the area is wetter, and thereport gives an account of \xhnt has been done in attempts to improxe the supply.

Nairobi. ‘ \\ ILLIAM PULFREX.lfith February. 1960. (.7wznn’mimzt‘r Ii ‘tI/HPV and Gym’ught‘].

CONTENTS

Abstract

I-Introduction

AGE

II-Physiography

III-Summary of Geology

IV-Details of Geology-

1. Basement System. .

1

2

2

(1) Calc-silicate rocks

(2) Biotite gneisses

(3) Quartzo-felspathic granulites

(4) Hornblende-biotite gneisses and plagioclase amphibolites2. Intrusive Rocks

3

3

(1) Quartz syenites

(2) Analcite syenites

(3) Porphyritic quartzsyenites . .

(4) Quartz microsyenite dykes

(5) Alkali microgranite dykes

(6) Tinguaite dyke. .

(7) Lamprophyre dykes

3. Fenites

3

4

4

5

5

syenites and medium to fine-grained quartz

4. Conglomerates, sands and lateritic deposits

5. Alluvial clays and silts

6. Superficial soils

V-Structure. .

VI-Mineral Deposits

1. General

6

6

7

7

7

8

9

9

10

10

11

11

11

12

2. Water

VII-References

MAP

Geological Map of the Endau Area (degree sheet 53, north-east quarter). Scale1 :125,000 . . . . . . . . .. At end

.;?

CONTENTS

Abstract

I-Introduction

AGE

II-Physiography

III-Summary of Geology

IV-Details of Geology-

1. Basement System. .

1

2

2

(1) Calc-silicate rocks

(2) Biotite gneisses

(3) Quartzo-felspathic granulites

(4) Hornblende-biotite gneisses and plagioclase amphibolites2. Intrusive Rocks

3

3

(1) Quartz syenites

(2) Analcite syenites

(3) Porphyritic quartzsyenites . .

(4) Quartz microsyenite dykes

(5) Alkali microgranite dykes

(6) Tinguaite dyke. .

(7) Lamprophyre dykes

3. Fenites

3

4

4

5

5

syenites and medium to fine-grained quartz

4. Conglomerates, sands and lateritic deposits

5. Alluvial clays and silts

6. Superficial soils

V-Structure. .

VI-Mineral Deposits

1. General

6

6

7

7

7

8

9

9

10

10

11

11

11

12

2. Water

VII-References

MAP

Geological Map of the Endau Area (degree sheet 53, north-east quarter). Scale1 :125,000 . . . . . . . . .. At end

.;?

(‘UNl'ilN'i‘S, MEI

r\Ds[1'§lCl

I—Immducliun . ‘ . llI—I’hpiugz'nphg , , ‘ , , 3

1H" Summary of Ciafllflg}, ‘ ,, IIV— nils of Ciculng}

IV Basement Spicm ‘ , , ‘ 7 3

('1) Cah;'~>i{:r;.t :1»;w V A 3(I) Bimilc gflcisxcx

(3) ewwfc}«3&1t gl'umzmm 3

L4) l{omblcndo—MwliIn; muiwcx‘ «M Dhiuiudimc min f

4—4A

Z. lmr‘usnc Rod“

H I Guam \‘_\CI‘J§IC\ 5

(I) Annlcilc sy'mitm 5(3) Pnrphyrlfl; qum‘tz, s;,(*rm‘;x :mcl H‘wcdimu 1» 41‘ I'L'

53~CHIZQS ‘ . , . , _ , (1

(~13 Quum/ miamycnitc dyku , , f(5) AlkaEi Imcz‘ogmrmc d} M5 , , , ?rm Tinguuitc dw‘s. 7(7) [,1121‘;[M‘flg‘hf~ N {11.1w 7

3 Fcnim , . ‘ . ‘ >34. Conglvmczzncx. mmix ‘md mum: xicmwim 7 _ k}

5‘ Ailmiul chm and NH , . ., ‘23

(N. Supcx'lici:tl wilx' , V . , 11"}\v"iStruum1'c . , , . . , , . , 10

V17 f\=linerul Depmih , ‘ . , ll

l‘ (icncml .7 ‘ . ‘ , . . ‘ 112. \\;1Iu' . . , _ E‘i

VII WR-ci'm'unccs . ‘ . , . 11

‘xl \l’

Geological Map of me Endmu A111: Moms; duct 53. rmrth-mal quartcm. Sal:1 131000 ‘ AL end

ABSTRACT

The Endau area is approximately 1,200 square miles in extent, and is enclosed by latitudes1° 00' and 1° 30' S. and longitudes 38° 30' and 39° 00' E.

The greater part of the area is a lightly dissected plain-the end-Tertiary peneplain-out of which rise three residual hill masses, of which Endau (4,387 feet) is the largest.

The oldest rocks, which are poorly exposed, are quartzo-felspathic granulites, biotitegneisses, calc-silicate rocks and hornblendic gneisses of the Basement System (Precambrian).Intrusive into these rocks are quartz syenites and analcite syenites, micro syenite and alkalinemicro granite dykes and lamprophyres-members of an acidic alkaline igneous suite. Locallyat the margin of the quartz syenite intrusions the quartzo-felspathic granulites are fenitized.

The surface of the end-Tertiary peneplain is locally underlain by poorly exposedconglomerates and sands.

No economic mineral deposits were discovered. An account of the water-supplyposition is given.

.......

ABSTRACT

The Endau area is approximately 1,200 square miles in extent, and is enclosed by latitudes1° 00' and 1° 30' S. and longitudes 38° 30' and 39° 00' E.

The greater part of the area is a lightly dissected plain-the end-Tertiary peneplain-out of which rise three residual hill masses, of which Endau (4,387 feet) is the largest.

The oldest rocks, which are poorly exposed, are quartzo-felspathic granulites, biotitegneisses, calc-silicate rocks and hornblendic gneisses of the Basement System (Precambrian).Intrusive into these rocks are quartz syenites and analcite syenites, micro syenite and alkalinemicro granite dykes and lamprophyres-members of an acidic alkaline igneous suite. Locallyat the margin of the quartz syenite intrusions the quartzo-felspathic granulites are fenitized.

The surface of the end-Tertiary peneplain is locally underlain by poorly exposedconglomerates and sands.

No economic mineral deposits were discovered. An account of the water-supplyposition is given.

.......

ABSTRACT

The lau arm is atppt'oxmmtel} LIOU squurc' miles in extent. tmtl is enclosed '03 latitudes1 00" and I 30 S.;mt1ltmgitutlcs SS 3 'l and 39 ()0 L

The greater part of the Lil'CLl l5 L1 ll:55

'htly dissected plain rlhc end—Tertiary pcncpluiniout of which rise tltrce rcsulunl hill ml ' s

Lc . ol‘ \xltich Entltltl H.387 feet) is the largest.

The oldest mqlm which are poorl) cw‘u’wsctl are qtutrtm-l'slspithic grunulltcs. biotitcgncisscs. calc- cute :1s and lwmblcmlia.‘ gncisscs of the Bttssmtnt System (Prccumbriun).Intrusive into muse :‘oclts are qum‘t/ swnitcs nml untilcltc 5) Ct ltcs. mlcmswnlte and alkalinemicmgrzmitc \lfl'GS and lummnpln;1‘cs HICTDl‘CI'S ohm :m'tlic alkallttc lgncous suite. Locallyat the margin of the quxmr sycnitv: intrusions the qLutrtw—l‘cispttthi5 gr‘nnulitcs arc l'cnitlzcd.

[“nc surface ml" thc cltd»TCt‘tl&1‘} psttt‘pltiln ls inmil} underlain by pearl} exposedconglomerates and >Llfld\.

_\0 economic mincml tlcpnslts were discmct‘cd‘ ;\11 :zcwtmt of thc \.\';ttc:‘—st1p_t)|_\posnion lS aivcn.

GEOLOGY OF THE ENDAU AREA

I-INTRODUCTION

A geological reconnaissance of the Endau area, the north-east quarter of Degree Sheet53 (Kenya; Directorate of Overseas Surveys, sheet 152), was carried out during August andSeptember, 1957. The area is bounded by the meridians 380 30' and 390 E. and by theparallels 1000' and 10 30' S., and is approximately 1,200 square miles in extent.

The western third of the area, west of a general line from the upper Matia river throughEngamba to Katumbi and beyond is part of the Endau location of Kitui district. Thegreater part of the remainder is included in the Eastern Crown Lands, which is also part ofKitui district. The north-east corner, including Kandelongwe hill, is in the Garissa districtof the Northern Province.

Only the vicinity of the Endau hills is populated, by Wakamba, and sporadic cultivationis carried on along the Munyoni river as far east as Katumbi. The upper parts of Endauhill were cultivated up to a few years ago, but the whole hill has now been declared a NativeForest. The Endau vicinity is noted for th~ good-quality native cattle it produces, but thereare no local industries or exports other than cattle.

Rainfall is low on the featureless plain, which comprises the greater part of the area,but is relatively high south-west of Endau-the rainfall at Endau during 1956 was 43.33inches, the average for the five years 1951-1956 being 35.03 inches. Long-term rain-gaugeswhich have recently been set up at Yendoboini and Sosoma (the latter north of the presentarea) suggest an annual rainfall of 10 to 15 inches in those areas.

Communications.-Two moderately good earth roads give access to Endau, one fromthe Garissa road via Nuu, and another from Kitui via Zombe. Both enter the area from thewest. From Endau rough motor-tracks pass north and south of Endau hill. The northerlyone is maintained as far as Makuka, but from there onwards is a rough narrow track con-tinuing past Engamba as far as Eyuku water-hole. A branch from this track passes north-wards from Engamba to Sosoma and finally to the Garissa road. The southerly motor-trackfollows the Munyoni river past Katumbi to Ngomano where it forks; one very roughbranch turns south and continues out of the area to the Thua river and Mutha. The othercrosses the Munyoni and forks again, one branch going as far east as Ngwaniwa water-hole,the other following the Nziu river to Makuka. Further tracks, from Sosoma and Ndeyini,enter the area in the north and give access to Kandelongwe. A motor-track also leadsnorthwards from Yanzeu water-hole in the north-eastern corner of the area and is said toconnect with the main Garissa road. All these motor-tracks are narrow and partly overgrown,and are often very rough where elephants have used them in rainy seasons. They are onlysuitable for small robust vehicles.

Maps.-The only existing maps of the area before the present survey were the 1:250,000South-A-37

Kitui Sheet No. and the 1:500,000 sheet S.A. 372, which show little beyondI

the outlines of the hills. The topographic detail on the geological map accompanying thisreport was compiled by the writer from air photographs, controlled by a plane-table survey.Areas not covered by air photographs were sketchily surveyed by plane-table and compassresection, and their representation is tentative. A notable feature of the plane-table workin the area was the difficulty of fixing positions in the featureless eastern half.

Previous Geological Work.-None of the early explorers who passed through the Kituidistrict seem to have visited the Endau area. Champion (1912, p. 15)*, however, referredin passing to phonolite that he had observed north-east of Endau. No phonolite was seenduring the present survey. In 1934 or 1935 W. D. Harverson obtained a specimen of syenitefrom a boulder near Endau.

The Kitui area to the west was surveyed by L. D. Sanders (1954). There is slight dis-crepancy between the maps of the Endau and Kitui areas in the vicinity of Endau village.This is probably due to surveying inaccuracies and personal variations in the interpretationof air photographs.

*References are quoted on p. 12.

10.. - .

GEOLOGY OF THE ENDAU AREA

I-INTRODUCTION

A geological reconnaissance of the Endau area, the north-east quarter of Degree Sheet53 (Kenya; Directorate of Overseas Surveys, sheet 152), was carried out during August andSeptember, 1957. The area is bounded by the meridians 380 30' and 390 E. and by theparallels 1000' and 10 30' S., and is approximately 1,200 square miles in extent.

The western third of the area, west of a general line from the upper Matia river throughEngamba to Katumbi and beyond is part of the Endau location of Kitui district. Thegreater part of the remainder is included in the Eastern Crown Lands, which is also part ofKitui district. The north-east corner, including Kandelongwe hill, is in the Garissa districtof the Northern Province.

Only the vicinity of the Endau hills is populated, by Wakamba, and sporadic cultivationis carried on along the Munyoni river as far east as Katumbi. The upper parts of Endauhill were cultivated up to a few years ago, but the whole hill has now been declared a NativeForest. The Endau vicinity is noted for th~ good-quality native cattle it produces, but thereare no local industries or exports other than cattle.

Rainfall is low on the featureless plain, which comprises the greater part of the area,but is relatively high south-west of Endau-the rainfall at Endau during 1956 was 43.33inches, the average for the five years 1951-1956 being 35.03 inches. Long-term rain-gaugeswhich have recently been set up at Yendoboini and Sosoma (the latter north of the presentarea) suggest an annual rainfall of 10 to 15 inches in those areas.

Communications.-Two moderately good earth roads give access to Endau, one fromthe Garissa road via Nuu, and another from Kitui via Zombe. Both enter the area from thewest. From Endau rough motor-tracks pass north and south of Endau hill. The northerlyone is maintained as far as Makuka, but from there onwards is a rough narrow track con-tinuing past Engamba as far as Eyuku water-hole. A branch from this track passes north-wards from Engamba to Sosoma and finally to the Garissa road. The southerly motor-trackfollows the Munyoni river past Katumbi to Ngomano where it forks; one very roughbranch turns south and continues out of the area to the Thua river and Mutha. The othercrosses the Munyoni and forks again, one branch going as far east as Ngwaniwa water-hole,the other following the Nziu river to Makuka. Further tracks, from Sosoma and Ndeyini,enter the area in the north and give access to Kandelongwe. A motor-track also leadsnorthwards from Yanzeu water-hole in the north-eastern corner of the area and is said toconnect with the main Garissa road. All these motor-tracks are narrow and partly overgrown,and are often very rough where elephants have used them in rainy seasons. They are onlysuitable for small robust vehicles.

Maps.-The only existing maps of the area before the present survey were the 1:250,000South-A-37

Kitui Sheet No. and the 1:500,000 sheet S.A. 372, which show little beyondI

the outlines of the hills. The topographic detail on the geological map accompanying thisreport was compiled by the writer from air photographs, controlled by a plane-table survey.Areas not covered by air photographs were sketchily surveyed by plane-table and compassresection, and their representation is tentative. A notable feature of the plane-table workin the area was the difficulty of fixing positions in the featureless eastern half.

Previous Geological Work.-None of the early explorers who passed through the Kituidistrict seem to have visited the Endau area. Champion (1912, p. 15)*, however, referredin passing to phonolite that he had observed north-east of Endau. No phonolite was seenduring the present survey. In 1934 or 1935 W. D. Harverson obtained a specimen of syenitefrom a boulder near Endau.

The Kitui area to the west was surveyed by L. D. Sanders (1954). There is slight dis-crepancy between the maps of the Endau and Kitui areas in the vicinity of Endau village.This is probably due to surveying inaccuracies and personal variations in the interpretationof air photographs.

*References are quoted on p. 12.

10.. - .

GEOLOGY OF THE ENDALT AREA

l—INTRODL'CTION

A ueologieal reeonnaissttnee of the Ehtlati area. the north—east quarter of Degree Sheet53 (Ken) 1; Direetorate of OVei‘seas Surveys. sheet 153) \\ ts L‘Liirieti 111 it during August andSeptember 1957. The area is hounded 1‘11» the tiieritliuns 35‘ 30 and -9 E. and b} theparallels 1 00111111 1 3LT 5.. and is unproxiittatel} 1.2008L‘1u1tre 11111125 in extent.

The western third of the area. west 01‘ 1‘; general line from the upper Malia river throughEngainha to Katumbi and beyond is hurt ot the Endau loeation ot' Kitui district. Thegreater part 01‘the remainder is inelutled in the Eastern (11m 11 lands. \\ hieh is 11150 part ofKitui district. The north—east corner. including Kantlelongwe hill. is in the Carissa districtttl‘ the Northe i1 P1o\iit1eL.

Oniy the x'ieinity nt' t‘1e [inlaa hills i\.' populated. 1.1:» \\';i}\'.1111h.3. and sporadie cultivationis carried on alongr the \1tllt}ttl‘li ri\er 1t; 1111' east as Katuttihi. The unher 1111115 (if EttdatthiEl were eultixated up to 1; ten years ugh. but the '11 hoi' 11111 has now been declared a NativeForest. The Endati \‘ieinity is hated tor the giJULl~qtitlliijv natiie eattle it produees. but thereare no local industries or exports other than eatt1e.

Ruiniali is low on the featureless 111.1111. 11 hieh Ltin‘iprises the greater part 111‘ the area,but is relqiti'uel} high south-“es: tit Entlaa . rthe taint111;tt 1.1111111: during 1956 was 433inehes. t51e merage tor the tire years 1951 1956 1cm: 35 1.13 Ertehes. L11 2 tet 11‘ rain-gaugeswhich h;i\e ree-.i;tly been set up. 111 \ endnboini 1111.1 Sosoma ithe hitter no: th ot the presentarea) suggest an annual rainfall of 10 to 15 inehes in those areas.

(UnlnlllflftYIN-(NM. iTwn 111111.1eratel}; gnotl earth roads ghe aeeess to Endau. one fromthe Garissa road 1111 Non. antl unwther tron: Kittii \ in Zonthe. Both enter the area from thewest. From Eridau rough '13111(11‘~II‘LECK§ pass north and south of Entlau 11i'tl. The northerlyone is :11;iiiit.;tinet as tar as Vakttka. but from there Linuar‘tls is Lt rough narrn'u. track eon-tit‘tuing pas: 1:11;;1111111 as 1111‘ ltS F.)i.11Lti '11 ater-hule. A branch 1111111 this t .L‘lL' 1111:..135 tiOI‘th-wards I‘rom Engamba to SOSUIN‘J 111111 tin 111) to the Carissa road. The southeriy motor-traekfollows the i\ilun_\‘oni ri\'er hast Katuinbi to Ngontano “here it torks; one may roughbranch turns \UULi‘l 111111 eontinties out 111' the area to the T111111 river and Mutha. The otherL‘rosses the \Iunwmi and fork» again. one hz'1meh gtiiizg 1t; 1111‘ east as Ngtt‘aniwa water—hole.the (\I‘ er t‘ollouing the N2111 :‘iier to .\11.1L'Lii<a. F er traeks. from 81.15311111 anti \Lleyini.enter the a in the north and gixe ueeess ti) K.it1tleli.1;1g\\e. ‘1:1‘t.11111-ti'.telL'..1<o leadsnorthuards l‘rmn tan/e11 .itei-hole in the :1 nth-eastern ertrne. tittthe are: and is said toeonneet with the main Carissa road. Allt he L motor tracks are 111111011 1111111111111; owigronnand are often very rough where elephants h1a\e used them in r1.in_x seasons. The} are onlysuitable 1111' small robust Vehieles.

Hap»: ~The only misting 111:1 ps ot the area ljetei‘e the present surx ey were the 1250.000South ~13

Kitui Sheet No. 7. 7r . 112111 the . :5011 (till >f1‘CC1 S. —\ 372 txhieh show little heyjnd1

the outlines ot the hills. The ttihogrtthhie detail on the getilogieal map :iL‘L'ompanying thisreport was compiled by the write: t'ront air phetour 1111s.etii1trt.illet1 b\‘ a t‘lflltC-1:11t SUI‘VCYAreas not em ere'L'1 h} air '1htittig: api is me. e skL tL'hilx \tt'\ 211-1111 111111e iahle anti Lmh')reseetion.1tnd their representatiiin is :entaiite . A 111111310 feature of tne ila:1e—.;th1e workin the area was the 111 lltL‘LllI) Ul tixiizg positions 1:1 the teatureless eastern halt.

PI'L"‘-'1"(H(.\.‘ (2111111191114 11 u.r'il.'.—\"t.\ne ot' the entiy e\i1iorers \\ hm passed through the KituiLlistriet seem '10 haxe Visited the F.ntt'.iu area. (.‘hanipion 11912. 11. 1511*. however. referredin passing to phonolite that he had ohsenetl north-east ot‘ Endau. No phonolite was seenduring the present suiaey. 111 193-1 or 1935. \\. D. Harxerson obtained a specimen of syenitefrom a boulder near Entiau.

The kittii area to the nest \ h stifleueti 115 1.. D. Sanders 1195—11. There is slight dis-erepane} heme-en 1.1L: mans 01111;“ 1:11L111u anLl Kittii areas in the \ieinit)‘ of 121111.111 \'iiEage.This is probably due to surreying inaeeuraeies and personal variations in the interpretationof air photographs.

'Refereiiees Lire .._ttLitL'L1 Lit; 1;, 12

2

The area to the north-the Ndeyini area, has recently been surveyed by J. B. Wright(report in preparation) and although the maps agree well as to topography there are minordiscrepancies in the interpretation of soil types.

II-PHYSIOGRAPHY

The greater part of the area consists of an almost featureless plain on which are shallowwidely-spaced valleys. Arising abruptly from this plain are three inselbergs-Endau(4,387 ft.), Engamba (3,100 ft.) and Kandelongwe (1,570 ft.). Of these Endau is by far thelargest and is a sub-circular hill mass seven miles in diameter divided centrally by two north-south valleys, the Sikati and the Ilimukuyu. Apart from these three upstanding hill massesthe only other notable features on the plain are small bald crags, no higher than 50 feetabove the surrounding country, such as Kinani and Siobiliwa.

The principal drainage system of the area is that of the Nziu river and its right banktributary the Munyoni. A further river is the Matia, which passes north of Engamba. TheNziu and Munyoni rivers, and some of the smaller ones also, have the broad flat alluvium-filled floors and meandering and braided courses characteristic of maturity. The valleyfloors are never more than 150 feet below the surface of the surrounding plain. The sidesof the Munyoni and Nziu valleys are indented by short tributary valleys of youthful profileand cross-section. If the profiles of the tributary valleys are projected into the main valleysbeneath the alluvium it seems that the alluvium is, in places, up to 100 feet deep, and thatit fills up approximately half the depth of the major valleys. Evidence that the alluvium isover 80 feet deep is provided by bore-holes (p. 12), for instance, at Ngomano. The matureappearance of the major valleys is, to some extent, due to recent aggradation.

The development of the valleys could have come about in the following manner: theend-Tertiary peneplain at its maturity had widely spaced valleys, shallower and with fewershort tributaries than those of the present day. Gentle eastward tilting of the peneplaininitiated a cycle of incision, deepening the main valleys and giving rise to youthful tributaries.Before this incision could proceed very far it was, however, halted by a change in the regimeof the drainage resulting in aggradation of alluvium. Excluding factors such as tilting,warping or volcanic damming of drainage, for which there is no evidence in this area, theaggradation must have taken place as a result of climatic change. Progressive desiccationwould convert perennial streams to tapering ones, resulting in the deposition of alluviumat the ends of the tapering streams, and, together with the development of strongly seasonalrainfall, alter the nature of the vegetation cover, and give rise to sheet erosion of valley sidesand the overloading of streams with sediment.

The extensive plain, which lies at an altitude of approximately 1,800 ft. and 1,200 ft.at the western and eastern margins of the area respectively, and has an average eastwardslope of 17 ft. per mile, is correlated with the end-Tertiary erosion surface of north-easternand eastern Kenya (Dixey, 1948, pp. 16-17; Sanders, 1954, pp. 6-7). Occurring as thinlayers on this erosion surface are deposits of conglomerates, pebble beds and colluvialgrits. A discussion of the deposition of these peneplain deposits is given at p. 9.

The even summits of the hills comprising the southern and eastern parts of Engambarepresent remnants of an erosion bevel standing at 2,200 feet. This bevel is some 600 feethigher than the level of the end-Tertiary peneplain nearby, and probably represents a remnantof the sub-Miocene peneplain. In the area to the west Sanders (1954, pp. 5-7) placed thesub-Miocene bevel high on the Nuu hills at 3,800-4,000 feet, 1,200 feet higher than theend-Tertiary surface. Some late Tertiary or Pleistocene movement certainly took place onthe Mutito fault, as Sanders (p. 5) suggests, but he nevertheless places the sub-Miocenesurface at the same elevation on both sides of the fault. The writer believes that the sub-Miocene bevel occurs at a level of about 3,200 to 3,400 on the Nuu hills. If this is correctit implies a post-Miocene movement on the Mutito fault of c. 800 feet, downthrowing to theeast.

ill-SUMMARY OF GEOLOGY

The oldest rocks of the area are quartzo-felspathic granulites, biotite gneisses, horn-blende-biotite gneisses and calc-silicate gneisses which occur in the Endau vicinity. Theseare ascribed to the Basement System and are of Precambrian age. Intrusive into the BasementSystem rocks are three quartz syenite bodies, probably stocks, and associated microsyenite

-._---._---

2

The area to the north-the Ndeyini area, has recently been surveyed by J. B. Wright(report in preparation) and although the maps agree well as to topography there are minordiscrepancies in the interpretation of soil types.

II-PHYSIOGRAPHY

The greater part of the area consists of an almost featureless plain on which are shallowwidely-spaced valleys. Arising abruptly from this plain are three inselbergs-Endau(4,387 ft.), Engamba (3,100 ft.) and Kandelongwe (1,570 ft.). Of these Endau is by far thelargest and is a sub-circular hill mass seven miles in diameter divided centrally by two north-south valleys, the Sikati and the Ilimukuyu. Apart from these three upstanding hill massesthe only other notable features on the plain are small bald crags, no higher than 50 feetabove the surrounding country, such as Kinani and Siobiliwa.

The principal drainage system of the area is that of the Nziu river and its right banktributary the Munyoni. A further river is the Matia, which passes north of Engamba. TheNziu and Munyoni rivers, and some of the smaller ones also, have the broad flat alluvium-filled floors and meandering and braided courses characteristic of maturity. The valleyfloors are never more than 150 feet below the surface of the surrounding plain. The sidesof the Munyoni and Nziu valleys are indented by short tributary valleys of youthful profileand cross-section. If the profiles of the tributary valleys are projected into the main valleysbeneath the alluvium it seems that the alluvium is, in places, up to 100 feet deep, and thatit fills up approximately half the depth of the major valleys. Evidence that the alluvium isover 80 feet deep is provided by bore-holes (p. 12), for instance, at Ngomano. The matureappearance of the major valleys is, to some extent, due to recent aggradation.

The development of the valleys could have come about in the following manner: theend-Tertiary peneplain at its maturity had widely spaced valleys, shallower and with fewershort tributaries than those of the present day. Gentle eastward tilting of the peneplaininitiated a cycle of incision, deepening the main valleys and giving rise to youthful tributaries.Before this incision could proceed very far it was, however, halted by a change in the regimeof the drainage resulting in aggradation of alluvium. Excluding factors such as tilting,warping or volcanic damming of drainage, for which there is no evidence in this area, theaggradation must have taken place as a result of climatic change. Progressive desiccationwould convert perennial streams to tapering ones, resulting in the deposition of alluviumat the ends of the tapering streams, and, together with the development of strongly seasonalrainfall, alter the nature of the vegetation cover, and give rise to sheet erosion of valley sidesand the overloading of streams with sediment.

The extensive plain, which lies at an altitude of approximately 1,800 ft. and 1,200 ft.at the western and eastern margins of the area respectively, and has an average eastwardslope of 17 ft. per mile, is correlated with the end-Tertiary erosion surface of north-easternand eastern Kenya (Dixey, 1948, pp. 16-17; Sanders, 1954, pp. 6-7). Occurring as thinlayers on this erosion surface are deposits of conglomerates, pebble beds and colluvialgrits. A discussion of the deposition of these peneplain deposits is given at p. 9.

The even summits of the hills comprising the southern and eastern parts of Engambarepresent remnants of an erosion bevel standing at 2,200 feet. This bevel is some 600 feethigher than the level of the end-Tertiary peneplain nearby, and probably represents a remnantof the sub-Miocene peneplain. In the area to the west Sanders (1954, pp. 5-7) placed thesub-Miocene bevel high on the Nuu hills at 3,800-4,000 feet, 1,200 feet higher than theend-Tertiary surface. Some late Tertiary or Pleistocene movement certainly took place onthe Mutito fault, as Sanders (p. 5) suggests, but he nevertheless places the sub-Miocenesurface at the same elevation on both sides of the fault. The writer believes that the sub-Miocene bevel occurs at a level of about 3,200 to 3,400 on the Nuu hills. If this is correctit implies a post-Miocene movement on the Mutito fault of c. 800 feet, downthrowing to theeast.

ill-SUMMARY OF GEOLOGY

The oldest rocks of the area are quartzo-felspathic granulites, biotite gneisses, horn-blende-biotite gneisses and calc-silicate gneisses which occur in the Endau vicinity. Theseare ascribed to the Basement System and are of Precambrian age. Intrusive into the BasementSystem rocks are three quartz syenite bodies, probably stocks, and associated microsyenite

-._---._---

IJ

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-.-

3

and lamprophyre dykes. These form the Endau, Engamba and Kandelongwe hills. Theyare tentatively regarded as of late Mesozoic age. The youngest rocks are the thin conglomer-ates and pebble beds occurring on the end-Tertiary erosion surface. These are regarded aslate Tertiary or early Pleistocene in age.

The geological history and succession in the area is summarized in the followingtabulation :-

Pleistocene and Recent

Late Tertiary (?) or earlyPleistocene (?)

Superficial soilsValley-fill clays

Slight erosionPebble beds and conglomerates

tI

~

~

Mid-TertiaryLate Mesozoic(?)

-Erosion and Peneplanation--Erosion and Peneplanation-Syenite intrusives with syenite and lamprophyre

dykesErosion

Folding and MetamorphismBasement System

Precambrian

IV-DETAILS OF GEOLOGY

1. Basement SystemExposures of metamorphosed gneissose and granulitic rocks ascribed to the Basement

System occur only in the western part of the area near Endau and west and north-west ofEngamba.

Such rocks as were seen are comparable with those occurring in the eastern part of thesouth Kitui and Kitui areas (Saggerson, 1957; Sanders, 1954) and in the Mwingi area(Crowther, 1957). Little structural and stratigraphic inference can be drawn from the poorexposures in the present area.

(1) CALC-SILICATE ROCKS

Two exposures of calc-silicate rocks were found, one on the north bank of the Munyoniriver at Kalungu, and the other one mile west of that locality. Both occurrences are of finelylaminated rocks with alternating layers rich in hornblende, epidote, calcite and felspar.

(2) BIOTITE GNEISSES

Biotite gneisses occur in the Kololo river immediately south-east of Endau, and on thesouth side of the Munyoni valley one and a half miles south-east of Katumbi. The Kololoriver rocks tend to have massive outcrops and contain lenticular pegmatite bodies. Theyare brown to buff medium-grained rocks with faint colour layering and a crude foliationdefined by biotite flakes. The Munyoni river rocks are fissile, but otherwise similar to thosedescribed.

Rocks which can be regarded as transitional between biotite gneisses and quartzo-felspathic granulites occur on Kinani rock and in isolated exposures one mile to the north.Here there are closely interbanded leucocratic granulites without biotite and more foliatedgneisses with biotite and locally hornblende. An example of the latter type which alsolocally shows a tendency to develop porphyroblastic felspars was collected from the top ofKinani rock (specimen No. 53/1004*). In thin section this rock is seen to contain porphyro-blastic microcline, minor twinned oligoclase, sparse brown biotite and much quartz.

(3) QUARTZO-FELSPATIllC GRANULITES

Owing to their massive structure and lack of foliation the quartzo-felspathic granulitestend to outcrop more often than other Basement System rocks in the area. A faint foliationis, however, sometimes apparent in these rocks, and is caused by beds of slightly varyinggrain size. An almost ubiquitous feature is the presence of titano-magnetite grains, whichlocally reach 1- cm. in diameter.

The only specimens of quartzo-felspathic granulites collected are from the northernand north-western margin of the Engamba syenite body, and are affected by metasomatism

*Numbers prefixed by 53 refer to specimens in the regional rock collections at the Mines and Geologica IDepartment, Nairobi.

,I

I

I

I

I

.I-

-.-

3

and lamprophyre dykes. These form the Endau, Engamba and Kandelongwe hills. Theyare tentatively regarded as of late Mesozoic age. The youngest rocks are the thin conglomer-ates and pebble beds occurring on the end-Tertiary erosion surface. These are regarded aslate Tertiary or early Pleistocene in age.

The geological history and succession in the area is summarized in the followingtabulation :-

Pleistocene and Recent

Late Tertiary (?) or earlyPleistocene (?)

Superficial soilsValley-fill clays

Slight erosionPebble beds and conglomerates

tI

~

~

Mid-TertiaryLate Mesozoic(?)

-Erosion and Peneplanation--Erosion and Peneplanation-Syenite intrusives with syenite and lamprophyre

dykesErosion

Folding and MetamorphismBasement System

Precambrian

IV-DETAILS OF GEOLOGY

1. Basement SystemExposures of metamorphosed gneissose and granulitic rocks ascribed to the Basement

System occur only in the western part of the area near Endau and west and north-west ofEngamba.

Such rocks as were seen are comparable with those occurring in the eastern part of thesouth Kitui and Kitui areas (Saggerson, 1957; Sanders, 1954) and in the Mwingi area(Crowther, 1957). Little structural and stratigraphic inference can be drawn from the poorexposures in the present area.

(1) CALC-SILICATE ROCKS

Two exposures of calc-silicate rocks were found, one on the north bank of the Munyoniriver at Kalungu, and the other one mile west of that locality. Both occurrences are of finelylaminated rocks with alternating layers rich in hornblende, epidote, calcite and felspar.

(2) BIOTITE GNEISSES

Biotite gneisses occur in the Kololo river immediately south-east of Endau, and on thesouth side of the Munyoni valley one and a half miles south-east of Katumbi. The Kololoriver rocks tend to have massive outcrops and contain lenticular pegmatite bodies. Theyare brown to buff medium-grained rocks with faint colour layering and a crude foliationdefined by biotite flakes. The Munyoni river rocks are fissile, but otherwise similar to thosedescribed.

Rocks which can be regarded as transitional between biotite gneisses and quartzo-felspathic granulites occur on Kinani rock and in isolated exposures one mile to the north.Here there are closely interbanded leucocratic granulites without biotite and more foliatedgneisses with biotite and locally hornblende. An example of the latter type which alsolocally shows a tendency to develop porphyroblastic felspars was collected from the top ofKinani rock (specimen No. 53/1004*). In thin section this rock is seen to contain porphyro-blastic microcline, minor twinned oligoclase, sparse brown biotite and much quartz.

(3) QUARTZO-FELSPATIllC GRANULITES

Owing to their massive structure and lack of foliation the quartzo-felspathic granulitestend to outcrop more often than other Basement System rocks in the area. A faint foliationis, however, sometimes apparent in these rocks, and is caused by beds of slightly varyinggrain size. An almost ubiquitous feature is the presence of titano-magnetite grains, whichlocally reach 1- cm. in diameter.

The only specimens of quartzo-felspathic granulites collected are from the northernand north-western margin of the Engamba syenite body, and are affected by metasomatism

*Numbers prefixed by 53 refer to specimens in the regional rock collections at the Mines and Geologica IDepartment, Nairobi.

,I

I

I

I

I

.I-

and ianiprophyi" dykes. These form the Endau. Enganiba and Kandelongwe hills. Theya re tentatively re rded as of Eat-e Mesozoic age. The youngest rocks are the thin conglomer—ates and pehble ocds occurring on the end-Tertiary erosion suri'ace. These are regarded aslate Tertiary or early! Pleistocene in age.

The geological history- and succession in the area is summarized in the followingtabulation:

Pleistocene and Recent Superficial soilsValleynfill clays

- - Slight erosionlate Tertiary {1’} 0;” L‘L‘tl'i) l’ebhle beds and conglomerates

Pleistocene ('3)-—|-'.rosioii and Pehepianation———-—

\-'lid—Tct‘tiary Erosion and l’enertlanation - —- —Late \lcsozoic i '.‘J Sycnitc intrusites saith syenite and laniprophyre

dy kes— Erosion

’recanihriaii Folding and .‘y-ietamorphismBasement System

l\'—DETAILS 0F GEOLOGY1. Basement System

Exposures ol‘ :iatamorpnosed gheissose and granuli‘ic ro" 's ascribed to the BasementSystem occur only in the western part oi the area near Fndau and nest and north-west ofFogamha.

Such rocks as were seer.- are comoarahle with those occurring in the eastern part of thesouth Kitui "iLl Ki ll areas [Sliggc‘ {957: Sande". 5954i and in the \1\\'itigi areatCTrO't‘icr. E95 . i. Little structural and stratigraphic inference can be drawn from the poorexposures in the present area.

[ll C'.\Lt'—51L:t'.\TL‘ RocicsTwo exposures ot'calc-._ ate rocks were found. or

I'lHJl‘ at Kalttngu. and the other one mile w” st oi th:laminated rocks with alternating layers rich in l’Ei.‘-I

e on the north bank of the Mtinyoni. tiity; Born occ irrerces are oifinely

nhende. epidotc. calcite and feispaifii2} Biorirr. ('i-xtzissrs

in t‘ie Kololo river immediately south—east of End-an, and on thee ol‘ the Munyoni valiey one and a half miles south—east of Katumbi. The Kololo

:‘iycr rocks tend to have massive outcrops and contain lenticular pegmattte bodies, Theyare brown to buff n‘icdiun‘i—graincd rocks with l‘ainl colour layering and a crude loliattondefined hy hiotite flakes. The Muny oni river rocks are fissile. hut otherwrse similar to thosedescribed.

Biotite an *isses oeet'"south

Rock's which can be regarded as transitional hetyxeen biotite grieisses and qtlartzo-t'elspathic granulites occur on Kinani rock and in i‘olatcd exposures one mile to the north.Here there are closely interbanded leucoeratic st... n ' es it'itliout biotite and more foil-atedgncisses uith biotite and locally hornblende. An example of the latter type which alsolocally shows a tendency to dotelop porphi't'tii‘ilastic I‘elsnars was collected i'rorn the top ofKinani rock (specimen No. 53 1004*}. in thin section this rock is seen to contain porphyro—hiastic microeline. minor twinned oligoc-..zse. sparse brown hiotite and much quartz.

t3} QL.-\it'izo-irr5miinc; CTR-met IE ':Owing to their massive structure and Each of t‘olizttion the quartrc-t'elspathie granulites

tend to outcrop more often than other Basement System rocits in the area. A faint lioliationis. however. sometimes apparent in these rocks. and is caused by beds of slightly varyinggrain size. An almost ubiquitous t'eature is the presence of titano-magnetite grains. whichlocally reach ‘- cat. in diameter.

The only speciiticns oi qttar‘L/o—leisoatliic gi'aiiuiites collected are ironi the northernand north-western margin of the Enganiha syenite body. and are affected by metasomatism

’3'\-'Ltr.i'ncrs Preiiscd hy 53 rei'cr i.'l " 1e region-.1 roel. enlieciions .i: the Mines and (icologxalDepartment. .\i‘.i"oiji_

4

associated with the formation of that body. With only a cursory examination of the rocksof the area around Mulanganga pan and along the north-western margin of Engamba itmight be difficult to separate the m'lssive quartzo-felspathic paragranulites from the fine-grained marginal parts of the syenite. The granulites are faintly foliated, however, andoften display a poor lineation. The abundance of quartz also differentiates them from theadjacent igneous rocks. Since the composition of all the Engamba granulites has beenaltered to a greater or lesser extent by felspathization asw:iated with the syenite intrusionthey are described later under the heading of fenites.

(4) HORNBLENDE-BIOTITE GNEISSES AND PLAGIOCLASE AMPHIBOLITES

A few exposures of hornblende-biotite gneiss occur in the Kakame river one and a halfmiles south-south-west of Endau village and are associated with finely banded plagioclaseamphibolites. These rocks continue into the Kitui area and have been described by Sanders(1954, pp. 27-28).

2. Intrusive Rocks

The hills Endau, Engamba and Kandelongwe are composed of syenitic intrusive rocks,which outcrop and weather into large rounded blocks. At some of the few places where themargin of the syenite bodies can be inferred with reasonable accuracy it is close to the baseof the hills. In the case of Endau and Kandelongwe the limit of the syenite exposurescorresponds closely to the margin of the intrusions. At Mulanganga and Kamuluyuni westof Engamba, however, syenites outcrop on the plain and give rise to distinctive white soilsfull of felspar cleavage fragments, and at these places the syenite boundaries can be inferredfrom the nature of the soil. Half-way between Kamuluyuni and Engamba, by the side ofthe motor-track, there is an area of similar white soil, but no exposures were seen there.It is possible that syenite or a similar rock underlies this soil.

The three principal syenite outcrops are much alike, both within and between them-selves. At the marginal parts of the Endau and Engamba bodies, however, are local develop-ments of a finer-grained facies, and locally this grades into a porphyritic facies. In theinterior of the syenites the only variations detected in the field were in grain size and thedegree of perfection of crystal form in the felspars. Outcrops are good on all the hills, butstream sections are generally poor, for the bouldery nature of the surface rocks results instreams being choked by heaps ~nd trains of transported rocks. Mapping in the hills ishindered by exceptionally thick bush below approximately 3,600 ft., but above this levelon Endau there is pleasant forest, which is inhabited by rhinoceros and buffalo.

The intrusive nature of the syenites is indicated by their composition and texture, andis confirmed by the occurrence of numerous microsyenitic dykes in the surrounding BasementSystem rocks. No evidence of ring structures or multiple intrusions such as are known fromcomparable intrusives in Nyasaland (Stringer et al., 1956, pp. 5-8) was seen, but the formof the Kandelongwe intrusion possibly suggests such structures.

Petrographically the intrusive rocks are quartz syenites comparable to perthosite andin the central part of Endau there is an analcite syenite. One of the Engamba specimens ismonzonitic. These rocks are closely comparable to several syenite intrusions in Nyasaland,such as the Chambe plateau ring complex (Stringer et al., 1956, pp. 11-18), and the Zombaand Mlanje syenites (Dixey et al., 1955, pp. 30-31), the latter being described as orthoclase-hornblende syenite. -

The commonest dykes in the Endau area are porphyritic microsyenites comparable tosolvsbergites. Others contain more quartz and are microgranites allied to grorudite. Threelamprophyre dykes were seen. The occurrence of alkaline dyke rocks and of fenites at themargin of the Engamba syenite suggests that the intrusives belong to an alkaline igneoussuite comparable with those that elsewhere contain such rocks as nepheline syenites andcarbonatites (see Dixey et al., 1955, pp. 36-40).

Direct evidence of the age of the intrusions is confined to the facts that they are youngerthan the Basement System folding (which is Precambrian) and older than the Miocene.The intrusions may be of late Mesozoic or Tertiary age like the Jombo alkaline igneouscomplex (Baker, 1953, pp. 32-48).

r..

4

associated with the formation of that body. With only a cursory examination of the rocksof the area around Mulanganga pan and along the north-western margin of Engamba itmight be difficult to separate the m'lssive quartzo-felspathic paragranulites from the fine-grained marginal parts of the syenite. The granulites are faintly foliated, however, andoften display a poor lineation. The abundance of quartz also differentiates them from theadjacent igneous rocks. Since the composition of all the Engamba granulites has beenaltered to a greater or lesser extent by felspathization asw:iated with the syenite intrusionthey are described later under the heading of fenites.

(4) HORNBLENDE-BIOTITE GNEISSES AND PLAGIOCLASE AMPHIBOLITES

A few exposures of hornblende-biotite gneiss occur in the Kakame river one and a halfmiles south-south-west of Endau village and are associated with finely banded plagioclaseamphibolites. These rocks continue into the Kitui area and have been described by Sanders(1954, pp. 27-28).

2. Intrusive Rocks

The hills Endau, Engamba and Kandelongwe are composed of syenitic intrusive rocks,which outcrop and weather into large rounded blocks. At some of the few places where themargin of the syenite bodies can be inferred with reasonable accuracy it is close to the baseof the hills. In the case of Endau and Kandelongwe the limit of the syenite exposurescorresponds closely to the margin of the intrusions. At Mulanganga and Kamuluyuni westof Engamba, however, syenites outcrop on the plain and give rise to distinctive white soilsfull of felspar cleavage fragments, and at these places the syenite boundaries can be inferredfrom the nature of the soil. Half-way between Kamuluyuni and Engamba, by the side ofthe motor-track, there is an area of similar white soil, but no exposures were seen there.It is possible that syenite or a similar rock underlies this soil.

The three principal syenite outcrops are much alike, both within and between them-selves. At the marginal parts of the Endau and Engamba bodies, however, are local develop-ments of a finer-grained facies, and locally this grades into a porphyritic facies. In theinterior of the syenites the only variations detected in the field were in grain size and thedegree of perfection of crystal form in the felspars. Outcrops are good on all the hills, butstream sections are generally poor, for the bouldery nature of the surface rocks results instreams being choked by heaps ~nd trains of transported rocks. Mapping in the hills ishindered by exceptionally thick bush below approximately 3,600 ft., but above this levelon Endau there is pleasant forest, which is inhabited by rhinoceros and buffalo.

The intrusive nature of the syenites is indicated by their composition and texture, andis confirmed by the occurrence of numerous microsyenitic dykes in the surrounding BasementSystem rocks. No evidence of ring structures or multiple intrusions such as are known fromcomparable intrusives in Nyasaland (Stringer et al., 1956, pp. 5-8) was seen, but the formof the Kandelongwe intrusion possibly suggests such structures.

Petrographically the intrusive rocks are quartz syenites comparable to perthosite andin the central part of Endau there is an analcite syenite. One of the Engamba specimens ismonzonitic. These rocks are closely comparable to several syenite intrusions in Nyasaland,such as the Chambe plateau ring complex (Stringer et al., 1956, pp. 11-18), and the Zombaand Mlanje syenites (Dixey et al., 1955, pp. 30-31), the latter being described as orthoclase-hornblende syenite. -

The commonest dykes in the Endau area are porphyritic microsyenites comparable tosolvsbergites. Others contain more quartz and are microgranites allied to grorudite. Threelamprophyre dykes were seen. The occurrence of alkaline dyke rocks and of fenites at themargin of the Engamba syenite suggests that the intrusives belong to an alkaline igneoussuite comparable with those that elsewhere contain such rocks as nepheline syenites andcarbonatites (see Dixey et al., 1955, pp. 36-40).

Direct evidence of the age of the intrusions is confined to the facts that they are youngerthan the Basement System folding (which is Precambrian) and older than the Miocene.The intrusions may be of late Mesozoic or Tertiary age like the Jombo alkaline igneouscomplex (Baker, 1953, pp. 32-48).

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4

(associated I'I'ith thc iornunioa of that body. With ml} a cursor): examination of the rocksof the are: '.IroIII1d \'l .‘Il'III- t-a :1ga I1'I' and alone the I1L'1I'Ih-western margin 01‘ Engamba itmight be di. I III sL' :1a L1Ihe n1' .si'Ie Lia-I1. 'I/I1- Ielspethie 1.1'I1IIIgIIIInLIlites hum the fine-gtaiited IIIIII'IZIIILI'. I'1I11'ts III we .1_\'eI1I:Ie. 'i'hL‘ gII.II IIliItes III'I'.‘ faintly Iolizitcd. hovt'II'exe . andoften display a poor lineation. The ahundanee oi qLIaI'I'z also difl‘erentiates them from theadjacent igneous rocks. Since the L'I1II1I1IIsiLiL1I1I Ul‘ III] the EIIgIIIt‘IbII gt'attulites has been'I'IIILz'eci to a greater or lesser esIeIII t1.) l‘elsI1'IIIhi/ation assosiazed With the syenite intrusiont|1e_\' are deseribed later under the heading of :‘enites.

III HIIIIs'III.rINDI:—I1Io'ri':'I-: L'isIEIssI-s Ixsu PL.-\{}l()('L.-5ISL .I\.‘r1|‘liiLi(')l_l'l'ES

A i'eIA e\IIL1sLII'es L'.1 i‘ hotIIbicride—l1it1tiie gnefss (wear in the KIIl-IIII11e I'i1.'er one and a hail‘miles south—s:1'IIti1—“'2': of Eadat'. \'iliI ge an d are associated with Iinel_\ banded 11lIILrioeiI1seItn'Inhibolites. These rocks LI1I1'IiIILIL1 i.IIIII the KituI :lrL‘Il IIIILl have been dLseI'ibed b}: SandetsI' 1954. 1111. 27-23}.

Intrusive Reel-Is

The hilis Endati EIIgaI'IIb'I :121Li KILI'ELlL’. L1I1L1\III: ate Lt1I11I1L15Ldo of ssenitie Intrusive I'oeks.“lllCh outcrop. ILI'I'Ll L'Ieatl'ier iII:I1 lIIrgL rounded blocks. .-'\t some oi the Few places where then'.'I1I;1n of .L1 sxenite bodies ean ' .1I'IeLl IIiIEI Ieas-1n'I1-Ibie accuracy it is close to the baseL11 the .1I.I'l.~,'. In t.1e ease of F: Li Kandelongue the limit of the syenite exposurescorresponds Closel) to the I'II'III'Lfin oi the Ii11I'IIsit1I1-.s. At .\"ILIlIII1gIIngII and KRIULIlL]}"LIfll westof En Itnba lIoI1L11'eI'. syenitcs oute.on on the I1l'IIiI'I and give rise to distinctive white soils

' 'es the 1_\'L‘I‘tiT.C boundaries can be inferred1L1t\\ LL1 K;t-.1.-L:l'.'~':'. 1:i and aIImba. by the side oi-

is ' '. sir. I: I' II' 11' i1i'.L1 mil out no exposures were seen there.at 11 Lane oI a siIni'IaI rock undeiiies thIs soil.

II'IIm the: I .[ITS ['I'ILJELII-l.It is possible

The three III'inI' much alike. both 11'. thi '.1 and oI1t\I'-'I en them—sel'I'es. \t thL I11: EI‘gIIInhII bI‘ILliLs. l1L1II-e\'Ie' . 'I'II" lt.1I'.'I1lLlL1elop—meIIts I1!“ II liIIL . lIx'Ii1is LII Ides Into a I1I1I'I1h11itie l‘aeies. III theinterior of the svenites tf‘te onlv VEII'lLl‘I iL.1 Is Ll tecte-II in IlIe Iield were in giain size and thcLnE'L‘L‘ I11' I1 ‘Il eetion ot LI'\s't:.'.! form i.1 the iLlsoaI's. Outerons are good on IIl'z the hills. butstreI'tII'I s ions at'e geneza'ly I}: ' l'oz' -'..1Ie boulder} I1I'.I.tI:'.e I1':' Ii1e .1'LI:'|‘aL'e rocks results instreams 3:1ei. I; ei'III‘seL'i by heaps 'IInd II'IIIIIs 'I'II‘ transported I'II-eks. .'\.‘[III1IIIIIg in the hills ishindered b_\- exceptionally {hick bush beioxx I1.;1.I1I'I.11IinIatL1l_\ 3.6100 ft.. but above this levelon FndIIu there is pleasant l'oi'es‘I. which is inhabited by rhinoceros and butT'I'Ilo.

The intrusive nature of the 1". e'IiIes is in'Ii '1is confirmed i.1\' the L1L1'L‘III'L'L.'IL1System rocks. .‘so eddenee I1|comparable intIIIsiI'es iI1{IF the KI-Indeinrieve i:1t:'

uteLi h)”.‘l1IeiI' L‘L1I11I1ositiL1I and testure andot :1I'I:1-. c: 'I1L.'-s :1.IcI'L1.s}L1:1iti'L1 d1'rI'es in Ihe suI rounding Basement

III;I structures or Inuitiolc intrusions suLh as are known I’Iom'1'I1Il'III1.Ll IStI'iIIgI'I ‘ III IIII.. l‘}_.(1. I111. 5—5.1} has seen. but the Form

I.1I1 I1I1s ' l; suggests such structures.

P; I: I1I1I III1I1Ieal|;I' IlIe iIIII'tIsiIe rocks are It‘IIIII'Iz s}enites Comparable to perthosite andin the L'enIIIII 11'III'I I1t" FnL’IaI: there Is an aI1ai'L'i=-.e sycnite. One of the Engamba specimens isntoneonitie. 'l'hese rocks an. L11 :sely 'L‘IIIl‘lP‘Lll'Ill'JiC LI1 seI'crai syeniie intrusions in Nyasaland.such as the Cl 1beI1‘Ia-‘Ieaa I I1. coI1-I'I :1.e .s ISII'iIIgCI' I-.-' III” 1956. I111. ll—lS}. III-1L".- the Zombaand ?\'il anie sI-enI. e.: [Dimy III I-I.-.. :955. .111. SIJ—-.‘1{I.ti1eiatteriaeine1 desei'ibed as orthoeIIIsc—hornblende syenite.

'l'i‘te c<1311i11.oI'Iest Ll)'l\'t"5 in the E! are 3.1LII'11l11'riIie I11iL'I'osyez1iLes L‘onInat'IIble IIIsélx'sbei'gites. Olltei's eL'I' 'IiI1 more quartz arid are out. ogranites allied to grorudite. Threelantpro;.1h_\'I"e dikes were seen. The oeL1=.II1:"I1I'I-:e IIJ‘ 'I-Il'II'aliIze dySIe rocks and ot' fcnit'es at theITI'IlI'gil‘l ot‘ the Engamha syenite suggests Ii1aI the intrusixes belong to an alkaline igneoussuite eon'tparahlc with those that elsewhere contain stIL‘h rocks as nepheiine syeI'Ii'les ande'III'bonaIiIes i1'III' Disc} L’I' II.I'.. {955. on. 36 401.

'DiIeet C\lClCl'|.CL'.' ol‘ the age oi the intrusions is L'IInIineL! to the l‘acts that the) are youngerthan the Basement System l‘oldinsz (which is I’I'cea I1l1i‘ian} and older than the Miocene.The intrusions may be ot l'i-e \'lesL1I1I1ie or TeIti'II'1' age like the Jombo alkaline igneousCOIIIplex {Bake}; [953. 1111.. ‘13 4:51.

5

(1) QUARTZ SYENITES

The quartz syenites are by far the commonest types in the three syenite intrusions. Theyare pale grey-buff rocks in which subhedral tabular felspars up to 10 mm. in length formnearly all the rock. Small clusters of ferromagnesian grains occur and interstitial quartzis sometimes visible in hand-specimen.

Specimens which typify the quartz syenites were collected at Kausia well and by thepipe-line one and a quarter miles north-north-east of Endau village (specimens 53/992 and53/994A respectively). They contain turbid perthitic alkali felspars up to 10 mm. long whichoften have sutured and intergrown margins. The orthoclase fraction of the perthite isinvariably more turbid and altered than the plagioclase; the latter is difficult to determine,but has a refractive index suggesting albite. Rarely the perthite has patches showing lamellaralbite twinning. In specimen 53/994A there are discrete small albite grains interstitially,and aggregates of a blue-green amphibole and a deeper green sodie pyroxene of low extinc-tion angle, probably aegirine. The hornblende is occasionally intergrown with a brownbiotite. Quartz occurs interstitially. Sphene is a common accessory mineral together withsmall amounts of opaque ore, probably magnetite.

The quartz syenite at Kamuluyuni wells (specimen 53/1006) is similar, but the perthiticstructure is coarser and albite patches in the perthite are more numerous. Biotite approaching

: he composition of lepidomelane is more common than green hornblende and apatiteoccurs rarely.

The eastern part of the Engamba intrusive is quartz syenite of the normal type (forinstance specimen 53/1006B from two miles west of Kalamba), but a rock obtained fromthe west of the summits, specimen 53/1008, differs in texture, being porphyritic. Subhedralperthite crystals with small brown biotite inclusions are common, the interstices beingcrowded with tabular oligoclase associated with sparse skeletal green hornblende up to 4 mm.across. Rare small quartz grains occur interstitially. Many of the hornblende grains aremarkedly zoned and are pleochroic in shades of pale greenish yellow to dark grey-blue.They have negative elongation and extinction angles up to 35° and are members of thearfvedsonite series. This rock tends to a monzonitic composition.

A syenite from Ekulungu, the southern part of the Engamba hills, differs from thosedescribed above. It is a medium-grained greyish brown rock (specimen 53/1013) with inequi-granular xenomorphic texture, consisting of turbid alkali felspar containing minute inclusionsof blue-green amphibole prisms. Hornblende also occurs as intergranular aggregatesassociated with ragged iron ore grains and apatite prisms. There is no quartz. This rockhas a texture suggesting slight crushing followed by limited recrystallization.

The Kandelongwe syenite contains more sodic plagioclase than the normal quartzsyenites. The orthoclase is often perthitic at grain margins and oligoclase occurs as discretegrains in intergranular spaces. Quartz is rare. In specimen 53/1015 acicular blue-greenhornblende occurs intergrown with some of the felspar along the principal cleavage. Theserocks are also monzonitic quartz syenites.

At the south-western extremity of the Endau syenite, in the valley half a mile south-eastof Kituka hill, the stream section exposes quartz syenite with numerous dark inclusions.The inclusions range from discrete blocks up to three feet in diameter down to minute specksand streaks. Frequently a streaky intermixture of the light syenite and dark fine-grainedrock is observed and there is abundant evidence that partial digestion of the dark xenolithshas taken place. The xenoliths are composed of dark fine-grained porphyritic rock ofbasaltic appearance. In a thin section of specimen 53/994B the rock is revealed, however, ascomposed of andesine microphenocrysts in a microcrystalline base of granular alkali felspar,aggregates of pale green chlorite intergrown with brown biotite, scattered iron ore grains andaggregates, and an abundance of opaque ore dust. No quartz was seen. This rock is anunusual variety of porphyritic microsyenite, unlike any other discovered in the area.

(2) ANALCITE SYENITES

Two specimens of analcite syenite were collected on Kauwaa, the eastern part of Endau.They are 53/1000 from Kibou spring and 53/1001 from half a mile west of Kauwaa summit.The type was not differentiated from the quartz syenites in the field and its distribution isconsequently uncertain. The analcite syenites are medium grey and darker in hand-specimenthan the typical quartz-syenites; in texture the two types are similar. Both specimens containmacroscopically visible pyrite.

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5

(1) QUARTZ SYENITES

The quartz syenites are by far the commonest types in the three syenite intrusions. Theyare pale grey-buff rocks in which subhedral tabular felspars up to 10 mm. in length formnearly all the rock. Small clusters of ferromagnesian grains occur and interstitial quartzis sometimes visible in hand-specimen.

Specimens which typify the quartz syenites were collected at Kausia well and by thepipe-line one and a quarter miles north-north-east of Endau village (specimens 53/992 and53/994A respectively). They contain turbid perthitic alkali felspars up to 10 mm. long whichoften have sutured and intergrown margins. The orthoclase fraction of the perthite isinvariably more turbid and altered than the plagioclase; the latter is difficult to determine,but has a refractive index suggesting albite. Rarely the perthite has patches showing lamellaralbite twinning. In specimen 53/994A there are discrete small albite grains interstitially,and aggregates of a blue-green amphibole and a deeper green sodie pyroxene of low extinc-tion angle, probably aegirine. The hornblende is occasionally intergrown with a brownbiotite. Quartz occurs interstitially. Sphene is a common accessory mineral together withsmall amounts of opaque ore, probably magnetite.

The quartz syenite at Kamuluyuni wells (specimen 53/1006) is similar, but the perthiticstructure is coarser and albite patches in the perthite are more numerous. Biotite approaching

: he composition of lepidomelane is more common than green hornblende and apatiteoccurs rarely.

The eastern part of the Engamba intrusive is quartz syenite of the normal type (forinstance specimen 53/1006B from two miles west of Kalamba), but a rock obtained fromthe west of the summits, specimen 53/1008, differs in texture, being porphyritic. Subhedralperthite crystals with small brown biotite inclusions are common, the interstices beingcrowded with tabular oligoclase associated with sparse skeletal green hornblende up to 4 mm.across. Rare small quartz grains occur interstitially. Many of the hornblende grains aremarkedly zoned and are pleochroic in shades of pale greenish yellow to dark grey-blue.They have negative elongation and extinction angles up to 35° and are members of thearfvedsonite series. This rock tends to a monzonitic composition.

A syenite from Ekulungu, the southern part of the Engamba hills, differs from thosedescribed above. It is a medium-grained greyish brown rock (specimen 53/1013) with inequi-granular xenomorphic texture, consisting of turbid alkali felspar containing minute inclusionsof blue-green amphibole prisms. Hornblende also occurs as intergranular aggregatesassociated with ragged iron ore grains and apatite prisms. There is no quartz. This rockhas a texture suggesting slight crushing followed by limited recrystallization.

The Kandelongwe syenite contains more sodic plagioclase than the normal quartzsyenites. The orthoclase is often perthitic at grain margins and oligoclase occurs as discretegrains in intergranular spaces. Quartz is rare. In specimen 53/1015 acicular blue-greenhornblende occurs intergrown with some of the felspar along the principal cleavage. Theserocks are also monzonitic quartz syenites.

At the south-western extremity of the Endau syenite, in the valley half a mile south-eastof Kituka hill, the stream section exposes quartz syenite with numerous dark inclusions.The inclusions range from discrete blocks up to three feet in diameter down to minute specksand streaks. Frequently a streaky intermixture of the light syenite and dark fine-grainedrock is observed and there is abundant evidence that partial digestion of the dark xenolithshas taken place. The xenoliths are composed of dark fine-grained porphyritic rock ofbasaltic appearance. In a thin section of specimen 53/994B the rock is revealed, however, ascomposed of andesine microphenocrysts in a microcrystalline base of granular alkali felspar,aggregates of pale green chlorite intergrown with brown biotite, scattered iron ore grains andaggregates, and an abundance of opaque ore dust. No quartz was seen. This rock is anunusual variety of porphyritic microsyenite, unlike any other discovered in the area.

(2) ANALCITE SYENITES

Two specimens of analcite syenite were collected on Kauwaa, the eastern part of Endau.They are 53/1000 from Kibou spring and 53/1001 from half a mile west of Kauwaa summit.The type was not differentiated from the quartz syenites in the field and its distribution isconsequently uncertain. The analcite syenites are medium grey and darker in hand-specimenthan the typical quartz-syenites; in texture the two types are similar. Both specimens containmacroscopically visible pyrite.

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‘JI

{I} QUARTZ SYFNITESThe quartz syenii'cs EI‘I3C . _‘.'.II I|.L‘ CUI‘HD'II'ITICN'l types in I.'IC ’

III‘C I‘I'IIIC gI'C}-—IILIII3 rocks III \\ II NLIbh‘C'LEI'III IIII‘F r I3C|%IIIICII.I'I_I- (Iii the rock. SrIIIIII Ci'LI‘3IL‘I53 II: IL‘:III:IIIIgIIc<i;III I:is SIIIIIcIimLIs \‘isiII'zL‘ in II:IIIII—\I‘;ILICII‘IIL‘II.

“CC \._\'C:‘I3l[i.‘ intrusions. TEICI'l. up 1.0 10 mm. in IL‘IIgt'II formins LILLLII' :Iii-LI Interstitial I.III'III‘II'.

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6

In thin section the analcite syenites are found to contain subhedral microperthite withsutured margins and occasionally showing carlsbad twinning. Refractive indices measuredon cleavage fragments fall in the range 1'522-1'532, which approximates to the range ofanorthoclase. The microperthite frequently contains crystals and aggregates of brownbiotite and more rarely of blue-green hornblende. Clusters of grains of sphene, greenhornblende and biotite occur, often with apatite and iron ore in addition. Analcite occursin turbid brown pools in intergranular spaces and in the felspars.

(3) PORPHYRITIC QUARTZ SYENITES AND MEDIUM- TO FINE-GRAINED QUARTZ SYENITES

Porphyritic quartz syenites and medium- to fine-grained non-porphyritic quartz-syenitesoccur marginally to the main intrusives as discontinuous bodies. Similar rocks occur withinthe Endau intrusion as small dyke-like masses, which however have irregular margins andlack chilled borders. The largest outcrops of these rocks are at the south-eastern extremityof Endau mountain and on the low hills immediately north-west of Engamba. The latterare invariably non-porphyritic.

These marginal rocks are only poorly exposed at the bases of the hills, but traversesalong the southern margin of the Endau body suggest that the porphyritic quartz syenitesare gradational into the quartz syenites of the main body, whereas the non-porphyriticquartz syenites, which often occur as discrete small bodies and probably dykes, may be theresult of a separate and slightly younger intrusive phase. Related dyke rocks occur plentifullyin the surrounding country, but are described separately.

The marginal quartz syenites differ from the main quartz syenite bodies only in grain-size and texture. They are pale grey-buff or pale brown rocks. Among the porphyriticquartz syenite exposures half a mile west of Koi a faint flow foliation was observed definedby similarly orientated small dark xenoliths up to half an inch long. At no place was apreferred orientation of felspar phenocrysts observed. Under the microscope the rocks areseen to have the same composition as the quartz syenites described above. A typical exampleis specimen 53/1003 from the base of Endau, north-north-west of Matundu. This rockcontains phenocrysts of perthite up to 12 mm. long and the matrix consists of subhedralperthite, rare tabular sodic plagioclase and interstitial quartz. Green hornblende is veryscarce and sphene is the only accessory mineral.

At the northern margin of Engamba, due north of the central summit, is a marginalzone of porphyritic quartz syenite approximately 50 yards wide. A specimen (53/1010)shows that the rock contains rather more sodic plagioclase than most examples of this type.Ore grains commonly occur as inclusions in the felspars and an aggregate of ore, spheneand apatite was observed. Hornblende sometimes occurs as uncommonly large skeletalcrystals.

(4) QUARTZ MICROSYENITE DYKES

Microsyenite dykes are common north-west and south-west of Endau, where they cutBasement System rocks. They are rarely more than two or three feet wide and are pale brownor pale grey rocks with sparse porcellaneous felspar phenocrysts up to 8 mm. long. Threeexamples may be mentioned, specimens 53/987 from the Nuu-Endau-Engamba road junction,53/990 from 300 yards east of Endau village shops, and 53/989 from the Kakame river Iimiles south of Endau village. Under the microscope the phenocrysts are seen to be turbidorthoclase-perthites are very scarce. In the first two specimens mentioned the matrixis composed of interfelted orthoclase prisms up to half a millimetre in length and smallamounts of interstitial quartz, but in specimen 53/989 quartz is much more abundant.Specimen 53/989 contains patches of sericitic mica and rare small crystals of a pale greenpyroxene. The other dykes contain opaque needles which are probably aegirine pseudo-morphosed by iron oxide.

A dyke of similar composition to those described, but containing xenoliths of quartzo-felspathic granulite, occurs on the north bank of the Nziu river 3 miles south-west ofKamuluyuni. A further dyke occurs on the Nuu-Engamba motor-track just east of the Nziuriver. This rock (specimen 53/1005) is reddish grey with numerous porcellaneous felsparphenocrysts up to one centimetre long. They are turbid orthoclase. The matrix consistsof microcrystalline spherulites of alkali felspar with interstitial quartz. Calcite and a brownamorphous mineral occur sparingly.

... - - --

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6

In thin section the analcite syenites are found to contain subhedral microperthite withsutured margins and occasionally showing carlsbad twinning. Refractive indices measuredon cleavage fragments fall in the range 1'522-1'532, which approximates to the range ofanorthoclase. The microperthite frequently contains crystals and aggregates of brownbiotite and more rarely of blue-green hornblende. Clusters of grains of sphene, greenhornblende and biotite occur, often with apatite and iron ore in addition. Analcite occursin turbid brown pools in intergranular spaces and in the felspars.

(3) PORPHYRITIC QUARTZ SYENITES AND MEDIUM- TO FINE-GRAINED QUARTZ SYENITES

Porphyritic quartz syenites and medium- to fine-grained non-porphyritic quartz-syenitesoccur marginally to the main intrusives as discontinuous bodies. Similar rocks occur withinthe Endau intrusion as small dyke-like masses, which however have irregular margins andlack chilled borders. The largest outcrops of these rocks are at the south-eastern extremityof Endau mountain and on the low hills immediately north-west of Engamba. The latterare invariably non-porphyritic.

These marginal rocks are only poorly exposed at the bases of the hills, but traversesalong the southern margin of the Endau body suggest that the porphyritic quartz syenitesare gradational into the quartz syenites of the main body, whereas the non-porphyriticquartz syenites, which often occur as discrete small bodies and probably dykes, may be theresult of a separate and slightly younger intrusive phase. Related dyke rocks occur plentifullyin the surrounding country, but are described separately.

The marginal quartz syenites differ from the main quartz syenite bodies only in grain-size and texture. They are pale grey-buff or pale brown rocks. Among the porphyriticquartz syenite exposures half a mile west of Koi a faint flow foliation was observed definedby similarly orientated small dark xenoliths up to half an inch long. At no place was apreferred orientation of felspar phenocrysts observed. Under the microscope the rocks areseen to have the same composition as the quartz syenites described above. A typical exampleis specimen 53/1003 from the base of Endau, north-north-west of Matundu. This rockcontains phenocrysts of perthite up to 12 mm. long and the matrix consists of subhedralperthite, rare tabular sodic plagioclase and interstitial quartz. Green hornblende is veryscarce and sphene is the only accessory mineral.

At the northern margin of Engamba, due north of the central summit, is a marginalzone of porphyritic quartz syenite approximately 50 yards wide. A specimen (53/1010)shows that the rock contains rather more sodic plagioclase than most examples of this type.Ore grains commonly occur as inclusions in the felspars and an aggregate of ore, spheneand apatite was observed. Hornblende sometimes occurs as uncommonly large skeletalcrystals.

(4) QUARTZ MICROSYENITE DYKES

Microsyenite dykes are common north-west and south-west of Endau, where they cutBasement System rocks. They are rarely more than two or three feet wide and are pale brownor pale grey rocks with sparse porcellaneous felspar phenocrysts up to 8 mm. long. Threeexamples may be mentioned, specimens 53/987 from the Nuu-Endau-Engamba road junction,53/990 from 300 yards east of Endau village shops, and 53/989 from the Kakame river Iimiles south of Endau village. Under the microscope the phenocrysts are seen to be turbidorthoclase-perthites are very scarce. In the first two specimens mentioned the matrixis composed of interfelted orthoclase prisms up to half a millimetre in length and smallamounts of interstitial quartz, but in specimen 53/989 quartz is much more abundant.Specimen 53/989 contains patches of sericitic mica and rare small crystals of a pale greenpyroxene. The other dykes contain opaque needles which are probably aegirine pseudo-morphosed by iron oxide.

A dyke of similar composition to those described, but containing xenoliths of quartzo-felspathic granulite, occurs on the north bank of the Nziu river 3 miles south-west ofKamuluyuni. A further dyke occurs on the Nuu-Engamba motor-track just east of the Nziuriver. This rock (specimen 53/1005) is reddish grey with numerous porcellaneous felsparphenocrysts up to one centimetre long. They are turbid orthoclase. The matrix consistsof microcrystalline spherulites of alkali felspar with interstitial quartz. Calcite and a brownamorphous mineral occur sparingly.

... - - --

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Dykes similar to those described above are recorded from the area to the west and weredescribed as porphyritic trachytes (Sanders 1954, pp. 33-34). In view of their compositionthere can be no doubt that these dyke-rocks are off-shoots from the main quartz syeniteintrusions of the Endau area.

The quartz micro syenites are comparable with s6lvsbergite dykes associated with theChilwa Series alkaline-igneous suite of Nyasaland (Dixey et al., 1955, p. 21) but have lesssodic plagioclase than typical s6lvsbergites (Johanssen, vol. III, pp. 107-109).

(5) ALKALINE MICROGRANITE DYKES

Three specimens of acid dykes proved on examination to contain a sufficient proportionof quartz to be termed microgranites. One of these (specimen 53/996) from a tributary ofthe Kalungu river, one and a half miles south-south-west of Kanguni spring, is a reddishgrey rock with quartz visible in hand-specimen. In thin section it is seen to be of mediumgrain with tabular euhedral altered perthite full of sericite, and rare sodic plagioclase. Quartzis well developed interstitially and forms approximately 20 per cent of the rock by volume.The quartz is accompanied by some fine-grained chalcedony. There are scarce ferromagnesiangrains, probably hornblende, and some sphene and iron ores.

A curious dyke occurs one mile north-east of Mulanganga pan as a body approximatelyone foot wide intrusive into quartzo-felspathic granulite. The margins of the dyke are highlyirregular as if the dyke had digested parts of the country rock. In hand-specimen (53/1019A)the rock is of basaltic appearance. In thin section, however, it is seen to be an acid rockconsisting of acicular aegirine rnicrophenocrysts in a matrix of myrmekitically intergrownquartz and microperthite. Clusters of rounded quartz grains and minute rods of a palegreyish blue to green mineral, possibly aegirine occur in the matrix.

In a thin section of the margin of this dyke the rock is seen to be fine-grained and flowbanded. The turbid felspars have a tendency to spherulitic structure, the spherulites beingarranged in bands. Between the spherulitic bands are trains of clear intersertal quartz grains.The margin of the dyke is locally ill-defined and appears to merge into the quartzo-felspathicgranulite forming the dyke wall. This granulite is substantially fenitized-the felspars areturbid and dominate the quartz in amount. The texture at the dyke margin suggests slightpenetration of dyke material into intergranular spaces of the metamorphic rock, followingmild alkali metasomatism.

A further quartz-rich dyke-rock was found near the northern margin of Engamba hillone mile north of the western summit. In thin section (specimen 53/1012) it is seen to havethe same texture as the quartz syenites. Tabular perthite crystals are abundant and clearquartz fills all intergranular spaces, forming approximately 30 per cent of the rock byvolume. Greenish brown biotite occurs as ragged books and sphene, magnetite and zirconare accessory.

These quartz-rich dyke-rocks are comparable with the riebeckite-microgranites (groru-dites) described from the Chilwa Series of southern Nyasaland (Dixey et al., 1955, p. 22;see also Johanssen, Vol. II, pp. 102-104).

(6) ANALCITE-TINGUAlTE DYKE

Only one rock of this type was seen, and this was found near the base of Endau mountainthree miles north-north-east of Kauwaa. It is a hard, almost flinty, dark grey-green rock offine grain. In thin section the rock (specimen 53/998) is revealed as microcrystalline withsmall acicular aegirine microphenocrysts in a base of alkali felspar laths. An isotropicmineral of low refractive index in interstices is probably analcite.

(7) LAMPROPHYRE DYKES

Two lamprophyre dykes were found in the Munyoni valley, 1.6 and 2 miles south-eastof Katumbi. A specimen of the eastern dyke (53/1021) has microporphyritic texture with1 to 2 mm. prismatic brown hornblendes and 1:mm. zoned augites in a fine-grained base ofsodic plagioclase with interstitial zeolite. Sphene occurs in association with iron ore. Therock is a vogesite.

A further lamprophyre dyke one foot wide occurs just outside the western margin ofthe area in the Kakame river, It miles south-west of Endau village. A specimen (53/988) con-tains numerous prismatic brown hornblende microphenocrysts in a matrix of basic plagio-clase full of acicular hornblende inclusions, olivine altered to calcite, iron ore and serpentine,and a meso stasis of isotropic zeolite. The rock is probably a camptonite.

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7

Dykes similar to those described above are recorded from the area to the west and weredescribed as porphyritic trachytes (Sanders 1954, pp. 33-34). In view of their compositionthere can be no doubt that these dyke-rocks are off-shoots from the main quartz syeniteintrusions of the Endau area.

The quartz micro syenites are comparable with s6lvsbergite dykes associated with theChilwa Series alkaline-igneous suite of Nyasaland (Dixey et al., 1955, p. 21) but have lesssodic plagioclase than typical s6lvsbergites (Johanssen, vol. III, pp. 107-109).

(5) ALKALINE MICROGRANITE DYKES

Three specimens of acid dykes proved on examination to contain a sufficient proportionof quartz to be termed microgranites. One of these (specimen 53/996) from a tributary ofthe Kalungu river, one and a half miles south-south-west of Kanguni spring, is a reddishgrey rock with quartz visible in hand-specimen. In thin section it is seen to be of mediumgrain with tabular euhedral altered perthite full of sericite, and rare sodic plagioclase. Quartzis well developed interstitially and forms approximately 20 per cent of the rock by volume.The quartz is accompanied by some fine-grained chalcedony. There are scarce ferromagnesiangrains, probably hornblende, and some sphene and iron ores.

A curious dyke occurs one mile north-east of Mulanganga pan as a body approximatelyone foot wide intrusive into quartzo-felspathic granulite. The margins of the dyke are highlyirregular as if the dyke had digested parts of the country rock. In hand-specimen (53/1019A)the rock is of basaltic appearance. In thin section, however, it is seen to be an acid rockconsisting of acicular aegirine rnicrophenocrysts in a matrix of myrmekitically intergrownquartz and microperthite. Clusters of rounded quartz grains and minute rods of a palegreyish blue to green mineral, possibly aegirine occur in the matrix.

In a thin section of the margin of this dyke the rock is seen to be fine-grained and flowbanded. The turbid felspars have a tendency to spherulitic structure, the spherulites beingarranged in bands. Between the spherulitic bands are trains of clear intersertal quartz grains.The margin of the dyke is locally ill-defined and appears to merge into the quartzo-felspathicgranulite forming the dyke wall. This granulite is substantially fenitized-the felspars areturbid and dominate the quartz in amount. The texture at the dyke margin suggests slightpenetration of dyke material into intergranular spaces of the metamorphic rock, followingmild alkali metasomatism.

A further quartz-rich dyke-rock was found near the northern margin of Engamba hillone mile north of the western summit. In thin section (specimen 53/1012) it is seen to havethe same texture as the quartz syenites. Tabular perthite crystals are abundant and clearquartz fills all intergranular spaces, forming approximately 30 per cent of the rock byvolume. Greenish brown biotite occurs as ragged books and sphene, magnetite and zirconare accessory.

These quartz-rich dyke-rocks are comparable with the riebeckite-microgranites (groru-dites) described from the Chilwa Series of southern Nyasaland (Dixey et al., 1955, p. 22;see also Johanssen, Vol. II, pp. 102-104).

(6) ANALCITE-TINGUAlTE DYKE

Only one rock of this type was seen, and this was found near the base of Endau mountainthree miles north-north-east of Kauwaa. It is a hard, almost flinty, dark grey-green rock offine grain. In thin section the rock (specimen 53/998) is revealed as microcrystalline withsmall acicular aegirine microphenocrysts in a base of alkali felspar laths. An isotropicmineral of low refractive index in interstices is probably analcite.

(7) LAMPROPHYRE DYKES

Two lamprophyre dykes were found in the Munyoni valley, 1.6 and 2 miles south-eastof Katumbi. A specimen of the eastern dyke (53/1021) has microporphyritic texture with1 to 2 mm. prismatic brown hornblendes and 1:mm. zoned augites in a fine-grained base ofsodic plagioclase with interstitial zeolite. Sphene occurs in association with iron ore. Therock is a vogesite.

A further lamprophyre dyke one foot wide occurs just outside the western margin ofthe area in the Kakame river, It miles south-west of Endau village. A specimen (53/988) con-tains numerous prismatic brown hornblende microphenocrysts in a matrix of basic plagio-clase full of acicular hornblende inclusions, olivine altered to calcite, iron ore and serpentine,and a meso stasis of isotropic zeolite. The rock is probably a camptonite.

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3. Fenites

Penites are produced from rocks of various compositions, but usually quartz-richintrusives or sediments, which have been altered by alkali metasomatism in proximity to analkaline igneous complex. African fenites and the fenitization process have recently beenreviewed by Campbell Smith (1950, pp. 208-212). In the present area the fenites are notwell exposed, for they occur on the plain at the margins of the syenite hill masses. They arebest developed around the northern and western margins of the Engamba syenite, at thenorth-eastern margin of Endau, and as inclusions or screens within the Endau syenite on theridge south of Kausia well. They are invariably derived from quartzo-felspathic granulitesof the Basement System and often closely resemble the non-porphyritic marginal quartzsyenites. They can, however, be distinguished from the syenites by the presence of relicfabrics such as foliation and, more often, lineation. Occasionally the fenitized quartzo-felspathic granulites develop a coarse-grained equigranular facies in which the felspars tendto tabular form. Such a rock is specimen 53/1007 from the foot of Engamba one mile northof the central summit. This rock contains turbid microperthite with crenulate margins.There is often a marginal zone of different composition adjacent to neighbouring quartzgrains. Rare oligoclase occurs in interspaces. Quartz is abundant as sub-round grains andinclusions in felspar. The felspars envelop the quartz grains forming the "net" texturecharacteristic of replacement. Small groups of greenish brown biotite crystals occur associa-ted with opaque ore grains.

A quarter mile west of the above locality a further specimen (53/1011) was collectedwhich is similar to that already described. In this rock, however, there are myrmekiticintergrowths between quartz and felspar.

Two further specimens (53/1017 and 53/1018) from outcrops in the stream by themotor-track one and a half miles north-north-west of Engamba central summit differ fromthose described in having notable amounts of perthite. A feature of all these rocks and indeedof the quartz syenites also is the turbid nature of the orthoclase or perthite, whereas theplagioclase and quartz is invariably clear. Specimen 53/1017 is similar to those alreadydescribed, but in specimen 53/1018 there is a notable advance towards igneous quartzsyenite texture and composition. The rock is composed mainly of interlocking turbid ortho-clase and microperthite grains; some of the latter are tabular in outline and show carlsbadtwinning. Rarely lamellar-twinned sodic plagioclase occurs at the margins of the potassicfelspar. Quartz is common but not as abundant as in the other fenites-it occurs as roundand irregular grains conspicuously partly replaced by felspar, or as narrow intergranularshards. Green-brown biotite, iron ore grains and euhedral sphene are the only other minerals.

Pale grey fine-grained rocks with saccharoidal texture were mapped on the Kituku-Kausia ridge at the western end of the Endau massif. A thin section of a specimen (53/993)taken from a point three-quarters of a mile south-west of Kausia shows the rock to be fenitizedquartzo-felspathic granulite differing from those described previously. The rock has equi-granular texture; approximately 80 per cent of the grains are of dusty alkali felspar, themajority of the remainder being quartz. There are scattered prismatic amphiboles, pleochroicfrom pale green to bottle green, and a brown to opaque mineral occurs with granules ofdoubtful aegirine and as intergranular films. The amphiboles are a sodic type with negativeelongation.

A specimen (53/999) from the northernmost of the two ovoid fenite outcrops at thenorth-eastern margin of Endau closely resembles quartz syenodiorite in composition. Thetexture is granular-interlocking, with a tendency for albite-oligoclase to develop as tabularcrystals. Dusty irregular orthoclase occurs, but is subordinate to plagioclase in amount andperfection of crystal form. Quartz is found interstitially and has ragged grains in process ofreplacement by felspars. Green hornblende and greenish brown biotite are present and aresometimes intergrown, while idiomorphic sphenes are plentiful. This rock is regarded as afenite on account of the texture, which is metamorphic rather than igneous. The abundanceof sodic plagioclase is notable.

At the northern foot of Endau mountain there are numbers of scattered exposures, someof normal quartz syenite, others of finer-grained rocks which can only be described asintermediate between syenite and quartzo-felspathic granulite, and which are fenites. Thelatter grade locally into porphyritic syenite-like rocks and these in turn, by developmentof a coarser matrix, grade into normal quartz syenites of the main intrusion. There is thus

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\

3. Fenites

Penites are produced from rocks of various compositions, but usually quartz-richintrusives or sediments, which have been altered by alkali metasomatism in proximity to analkaline igneous complex. African fenites and the fenitization process have recently beenreviewed by Campbell Smith (1950, pp. 208-212). In the present area the fenites are notwell exposed, for they occur on the plain at the margins of the syenite hill masses. They arebest developed around the northern and western margins of the Engamba syenite, at thenorth-eastern margin of Endau, and as inclusions or screens within the Endau syenite on theridge south of Kausia well. They are invariably derived from quartzo-felspathic granulitesof the Basement System and often closely resemble the non-porphyritic marginal quartzsyenites. They can, however, be distinguished from the syenites by the presence of relicfabrics such as foliation and, more often, lineation. Occasionally the fenitized quartzo-felspathic granulites develop a coarse-grained equigranular facies in which the felspars tendto tabular form. Such a rock is specimen 53/1007 from the foot of Engamba one mile northof the central summit. This rock contains turbid microperthite with crenulate margins.There is often a marginal zone of different composition adjacent to neighbouring quartzgrains. Rare oligoclase occurs in interspaces. Quartz is abundant as sub-round grains andinclusions in felspar. The felspars envelop the quartz grains forming the "net" texturecharacteristic of replacement. Small groups of greenish brown biotite crystals occur associa-ted with opaque ore grains.

A quarter mile west of the above locality a further specimen (53/1011) was collectedwhich is similar to that already described. In this rock, however, there are myrmekiticintergrowths between quartz and felspar.

Two further specimens (53/1017 and 53/1018) from outcrops in the stream by themotor-track one and a half miles north-north-west of Engamba central summit differ fromthose described in having notable amounts of perthite. A feature of all these rocks and indeedof the quartz syenites also is the turbid nature of the orthoclase or perthite, whereas theplagioclase and quartz is invariably clear. Specimen 53/1017 is similar to those alreadydescribed, but in specimen 53/1018 there is a notable advance towards igneous quartzsyenite texture and composition. The rock is composed mainly of interlocking turbid ortho-clase and microperthite grains; some of the latter are tabular in outline and show carlsbadtwinning. Rarely lamellar-twinned sodic plagioclase occurs at the margins of the potassicfelspar. Quartz is common but not as abundant as in the other fenites-it occurs as roundand irregular grains conspicuously partly replaced by felspar, or as narrow intergranularshards. Green-brown biotite, iron ore grains and euhedral sphene are the only other minerals.

Pale grey fine-grained rocks with saccharoidal texture were mapped on the Kituku-Kausia ridge at the western end of the Endau massif. A thin section of a specimen (53/993)taken from a point three-quarters of a mile south-west of Kausia shows the rock to be fenitizedquartzo-felspathic granulite differing from those described previously. The rock has equi-granular texture; approximately 80 per cent of the grains are of dusty alkali felspar, themajority of the remainder being quartz. There are scattered prismatic amphiboles, pleochroicfrom pale green to bottle green, and a brown to opaque mineral occurs with granules ofdoubtful aegirine and as intergranular films. The amphiboles are a sodic type with negativeelongation.

A specimen (53/999) from the northernmost of the two ovoid fenite outcrops at thenorth-eastern margin of Endau closely resembles quartz syenodiorite in composition. Thetexture is granular-interlocking, with a tendency for albite-oligoclase to develop as tabularcrystals. Dusty irregular orthoclase occurs, but is subordinate to plagioclase in amount andperfection of crystal form. Quartz is found interstitially and has ragged grains in process ofreplacement by felspars. Green hornblende and greenish brown biotite are present and aresometimes intergrown, while idiomorphic sphenes are plentiful. This rock is regarded as afenite on account of the texture, which is metamorphic rather than igneous. The abundanceof sodic plagioclase is notable.

At the northern foot of Endau mountain there are numbers of scattered exposures, someof normal quartz syenite, others of finer-grained rocks which can only be described asintermediate between syenite and quartzo-felspathic granulite, and which are fenites. Thelatter grade locally into porphyritic syenite-like rocks and these in turn, by developmentof a coarser matrix, grade into normal quartz syenites of the main intrusion. There is thus

I

L---

FenitesFenites are produced l‘t'tim rocks '1‘1‘ various C0n111t.15iti111‘.5.. hut u.5ue.tll_\ quart/r—I‘ich

intru5iV'L‘5 or setiit11ent5i. which hLlVC been altered. h_\' trlkuli n1; 111511111: tti5r11 in Frt'.)\'iil‘. it\ to analkaline igne11u5 enm 1le\'. Atrietin tenites "111d the l‘enitization i110 5l1111e recently beenre\'ie1\edtby { LUMP bell Smith tl‘)50. 1111. 20% 2l_'1.li1 the 1.11'e5'e11t Melt the Senites aree'ntitwell L‘xpOSCd. for thC_\ occur Oil the plain ut the tnzirgim 01‘ the .5}.e:1ite hill 111:1.‘551e5‘. lhe) [11'sbest (iC\ClOp=:(l zu'tnind the northern 11nd \i'e5tern in: gins L11 the 1:11;;11111‘111 .5 enite. :'.t the1101th —‘u.‘51ern margin otEntl11u. :1nti115it1el' 5i01‘15 02' 5Lreet15 \rx itltin the L '. ‘nite on the:itige south ol lxttusi111 well. ’t61 the lt‘i\tti‘lttl‘\lj~' derived from Lititti'tjlt1-i'el.. hie 3.1 unu.1tL.\111‘ the Basement Sy5‘tem and ol‘ten elu5el) resemble the non— i111i'1hx'r'itiL 11 u'ginal qua. r17Syenites. They eun. however. be (llStll‘H zi5heLi from the .5 e11ite5 bx the ptesenee ot ielieinbt‘ies Such 115 lVOlitttiOn and. mere (1 Ln. lineution. (.V)et.11‘ii.111;tll_x the teniti/etl (.[Lt'dt‘LZO-l‘elspztthie grtmtilit e5 Lle\' ”L111 11 e0111'5er11int‘el equi~ untiltir ttteie5 in 1\hiLl1 the lVelSp'atr5 tendto tabular ttrm. Sueh 11 ioek i555g1eeimen 53 ‘1007 t '1111the t‘t'toteit‘tnguntbn one t11ilenui'thof the central summit. ll1i5 ittek Ltmtuins turbiti mi L‘tupeithite with et'en ulute murgins.There is often 11 marginal zone (11 unit-rent eunzpmition tidiueent tu neighbuuting quartzgruim. Rare L1lig11el115'e meeur5 in inter5p:tee5‘. Quartz is abundant 115" Sub—round 95111115 andinelusions in t‘el5pttz'. the lVel51111r5 emelop the quartz grains forming the “net" tenurecharacteristic of repltteement. Small grt'11m5 11f 3;:Le11i5'l1 bi 1.1V'n biotite C]}SI1‘.lS meet: 1 assoeiu—tL‘ti with opaque ore gruin5.

,_.

-\ quarter mile \1'e5t of the ubute loettiit}: .1 l‘uz'ther Speeirnent 53‘ Hit ll \\;15 collected\xl'tit'h i5 5imil11r tn that already tle5e1'ibeti. in tl115 rock. hummer, there tire 1‘1131'111ekitieinteigrowth5 between Liuurt/ 11nd t‘el5pt1r.

Two further specimen“ 3. l0lT :tnd 53 lOlSi from 1:1uterot‘c. in the stream by themutant: 'ek one and 11 it 11ll‘ m: l'Ls 111’1t'ti1-11t1rtl'1-\'.'e5‘t (it axtmbtt central 5'ummit tlit'l‘er l‘rnntthuse de5ei‘ibetl in lit \' inu notable :11110'111‘15 Ol perthite. A lVeLtture‘ utttll the5e 2'11L'lL5 and indeedof the quartz :5yenite5 ul5u is the ttubztl nattue ot the orth OClLtSC or pet'thite. “ltct'CtlS theplagioelztse and quartz i5 irnttriubl} elettr. Speein‘en 531 i701 15 5imil: 1' to those ttlreutl}described. but in 511eeimen 53 10th there is '.1. nutuble Cttl\‘dflCC 1m» :05 igneous LlLtitt'lL5x'enite texture 11nd eo:11;nw5ition.Tl1e ruck i5 eumtmsed tnztini} t' l inter l0; 111111.} tut bid fll‘tl‘tD‘L'l115e 11nd mieropettthit e et'ii11515r1tne of the l.ttte1' :11'etztbul11r in 01: line :1110 5.l111\\'e:‘.1‘15l.1:ulthinning. R11 tel) lLEIT‘lCllLL-lWll‘dlCLl .5'1.'1Liie pl11«'t'1L'l:t'5e t1eeut'5 :11 the i'git15 t‘l the 1.111111. iet‘el5pur. Quttrt/ i5 eommnn but 111.11 :15 abundtu‘n :15 in the other t‘enite5 it ueeur5 :15 roundand irregular 131111115 constneuriusl} mutt) rep}: teetl l7\ telsptu «:11' 115 narrow intergrtutulur5h111'115. (green—brown biotite. iron ore grunts.1111Lte11hztl115'1l.phene:uet‘teonlyotherminei'tl5

Pale gtee» tine—grained rnel\5 with 5tteehtn't1itl111 texture were mnhhetl on the Kituku-Kuu5i1'1 riti 'L‘ztt the ‘x'e5tern enti 1.1:Vt he End 111 111115.5il‘. .\ thin 5eetit111 of :1 5tjeeime11 [53 993]taken [VT 11111 '.1 point thi ee- .t;ii te: 5 min mile south- \x e5t (1t Ktttzsiu Slums the fuck [(1 he I‘Cniii/Ldquut'tzo le l51111tl1 iL‘ utunulite Lil tier. ng lrt1t.1 111115e Lle5e1ibetl t1 ‘L‘VO‘tRlV the rock ht15 equi-L’T'U‘ltiliti‘ tt‘\tt11‘e: tlp‘l‘ll.‘\lllllllk.lj~ bl tut“ CL 1t (11 the g.11i:15' :1' e 1.11'lu5t\';1ll1;1litel5pz1r themilittfih (11 the min tintlei beiner qtl 11t Tl1e1e LttC 5e:tttttetl 11:'i 111 ttie '.1111i1hib11le 5 plettehroie110m pale green to 1‘t1ttle green. :tntl 11 known to 0;.111m 11: 1111111111111 t1eettt'5 v ith granules 01"tltnlbtt‘ul ttegirine 11nd 11.5 intergrunulur tiltns. The umtl1ibule511re 11 5L1Clietxpe with negativeelongation.

.»-\ 511eeimen (53 999] l‘i'nm the :1111'the1‘11n1ost 1:11“ the t\\.:' wraitl t'enite mutemm 111 thenurtlremtern margin 11't Enduu {heel}, re5emble5‘ quartz 5yent'1L'tiori1e in composition. Thetexture is. granulnr-interlueking. with '.1 ICl‘iLllL‘) t‘nr 11lt1ite-o} "1el.15e to de'i'e1011 :15 tubularery51uls. 01151} irregular urthueltme ueeurs. but 1.5 51.1l.1t1rtiin.1te11.1plugn‘rL " in amount andpei'l‘ectiun t1l'L'i'}5t:tl “ti-Ill. Qutti't/ i5 lountl int L‘r5t3tittll'. "ntl l1'15 rugged grains in 1111112655 atreplacement by t‘el511tu'5. Green hurrihlentte :1nti 1ee1155.1 l 1111111 biotin tire :nresent and are511111etime5 intet'grown. \\l1t1e iLlimno 'nhie whenes :ize pietniiui, thi5 reek is regarded :15 11JVenite (.111 :tceuunt 1.11 the texture. 11 111t i5: tnettutnn'nhie :‘1ttl‘1L‘t' 121.111 igneeua The abundanceof sodie plugioeltme is nt'itt'tble.

F

At the northern Foot of ttiduu mountain there are 11 1111l1e:'.5 11‘ 5ett‘1tet'etl exposure5or normal quartz 5yenite. utl1er5 Of tiner 111111.11 1'11 155' \1'ht l1 L"'.111 onl) be described 115'intermediate bet\\een 5yenite :mtl qut1:'t7t.1-1L mthie gittnulite. amt uhieh til'C t‘enites. Thelatter grade ioeztll} into porplnritie 5}’enite—iil<e rocks and tite5'e in ttu'n. by developmentof '.1 coursei‘ ittt‘ttrix. gt‘ttt‘le into normal L;'.i.t:'t/ 5:.enfte5‘ of the :iittii'. i1:'.i't.:.5i11:i. ll‘tL‘i'C is thus

(11110

9

a suggestion that there is a complete gradation between intrusive rocks and fenites of variouskinds. Owing to the scattered nature of the exposures and the rapid variation of rock typesthe geological boundaries in this part of the area are necessarily tentative.

The fenites from the northern and north-western margin of Engamba are notable inlacking aegirine and soda-amphiboles such as characterize almost all fenites. The develop-ment of turbid and replacive alkali-felspar at the expense of quartz is, however, characteristicof fenitization (see Campbell Smith, 1956, pp. 208-212).

4. Conglomerates, Sands and Lateritic DepositsThere is indirect evidence that much of the featureless plain that exists over most of the

area is underlain by sediments. The extreme scarcity of exposures, even on the sides of theshallow valleys, and the occurrence of float pebbles and gritty transported soils on somevalley sides suggest that the peneplained surface of Basement System rocks is overlain by athin sedimentary cover.

Exposures of conglomerates are most numerous on the sides of the Matia valley nearthe crossing of the Sosoma-Engamba motor-track. Here weakly-cemented poorly-sortedconglomerates with quartz and pegmatite pebbles up to four inches in diameter are exposed,with a thickness of up to twenty feet. Other exposures and pebble accumulations werefound at various scattered localities. The Engamba-Eyuku motor-track, for example,below the north face of Engamba runs just to the south of a low bank on which are abundantloose pebbles. The survey station at 1,550 feet three and a half miles south-east of Twambuiis situated on a mound of quartz pebbles. Good exposures of brown conglomerates devoidof bedding occur on the rise to the plain on the south bank of the Munyoni river two mileswest-south-west of Msemei water-hole. Scattered occurrences of pebble float in quartzosesoils are found along the sides of the Nziu and Munyoni valleys from Makuka and Katumbias far as Ngwaniwa and beyond. Generally speaking, the evidence suggests that thin con-glomerates and sands occur underlying the greater part of the area marked as covered byreddish brown sandy soil and the clay soils of the plains.

Boulders of cellular ironstone and small exposures of colluvial poorly-sorted grits withironstone zones and cappings occur frequently at the margins of the hills at the level of theplain. The better exposures are at the base of Engamba hill one mile east-north-east of theeastern summit, where exposures in a stream section show felspar grains in an iron stainedmatrix of sand and silt. These beds are at a slightly higher level than the heaps of quartzpebbles that occur on the pediment a little further to the north. At the base of the south faceof Kalongola are further grits co10ured pale grey, brown and reddish brown, and cappedby cellular ironstone. On the Endau-Makuka motor-track immediately north and north-westof Syuu dam there are scattered boulders of cellular ironstone, and similar boulders arecommon near Mulanganga water-hole. Sheets of loose ironstone nodules are common onbuff and reddish-buff sandy soils on the pediment slope at the north-east margin of Endauand at the south foot of Kituku hill, near Endau village.

Following the completion of the most recent peneplanation in the area it seems thatthin sheets of conglomerate were spread widely over the present and adjacent areas (they havebeen seen by the writer in the areas to the west and north). Sands were also deposited andgently sloping alluvial and colluvial material deposited at the bases of hill masses. Thesedimentary episode seems to have ended in the formation of widespread ferruginous surfacelaterite. The conglomerates must have been deposited under torrential conditions and theclimate generally was probably arid, for any sort of continuous vegetation cover wouldhave prevented widespread deposition.

The age of the beds can only be inferred in a general way from the erosional history ofthe whole of eastern Kenya, for no fossils have been found in them. The beds occur on theend-Tertiary peneplain of Northern Kenya (Dixey 1948, pp. 16-17) and incision by riversinto this surface in other areas is dated roughly as lower Pleistocene on the basis of artifactdiscoveries (op. cit. p. 17). The beds in the present area are regarded as latest Tertiary orearly Pleistocene in age.

5. Alluvial Clays and Silts

Following the deposition of the conglomerates, sands and laterites described above,there was a short period of incision of the drainage around the margins of the hills and along

9

a suggestion that there is a complete gradation between intrusive rocks and fenites of variouskinds. Owing to the scattered nature of the exposures and the rapid variation of rock typesthe geological boundaries in this part of the area are necessarily tentative.

The fenites from the northern and north-western margin of Engamba are notable inlacking aegirine and soda-amphiboles such as characterize almost all fenites. The develop-ment of turbid and replacive alkali-felspar at the expense of quartz is, however, characteristicof fenitization (see Campbell Smith, 1956, pp. 208-212).

4. Conglomerates, Sands and Lateritic DepositsThere is indirect evidence that much of the featureless plain that exists over most of the

area is underlain by sediments. The extreme scarcity of exposures, even on the sides of theshallow valleys, and the occurrence of float pebbles and gritty transported soils on somevalley sides suggest that the peneplained surface of Basement System rocks is overlain by athin sedimentary cover.

Exposures of conglomerates are most numerous on the sides of the Matia valley nearthe crossing of the Sosoma-Engamba motor-track. Here weakly-cemented poorly-sortedconglomerates with quartz and pegmatite pebbles up to four inches in diameter are exposed,with a thickness of up to twenty feet. Other exposures and pebble accumulations werefound at various scattered localities. The Engamba-Eyuku motor-track, for example,below the north face of Engamba runs just to the south of a low bank on which are abundantloose pebbles. The survey station at 1,550 feet three and a half miles south-east of Twambuiis situated on a mound of quartz pebbles. Good exposures of brown conglomerates devoidof bedding occur on the rise to the plain on the south bank of the Munyoni river two mileswest-south-west of Msemei water-hole. Scattered occurrences of pebble float in quartzosesoils are found along the sides of the Nziu and Munyoni valleys from Makuka and Katumbias far as Ngwaniwa and beyond. Generally speaking, the evidence suggests that thin con-glomerates and sands occur underlying the greater part of the area marked as covered byreddish brown sandy soil and the clay soils of the plains.

Boulders of cellular ironstone and small exposures of colluvial poorly-sorted grits withironstone zones and cappings occur frequently at the margins of the hills at the level of theplain. The better exposures are at the base of Engamba hill one mile east-north-east of theeastern summit, where exposures in a stream section show felspar grains in an iron stainedmatrix of sand and silt. These beds are at a slightly higher level than the heaps of quartzpebbles that occur on the pediment a little further to the north. At the base of the south faceof Kalongola are further grits co10ured pale grey, brown and reddish brown, and cappedby cellular ironstone. On the Endau-Makuka motor-track immediately north and north-westof Syuu dam there are scattered boulders of cellular ironstone, and similar boulders arecommon near Mulanganga water-hole. Sheets of loose ironstone nodules are common onbuff and reddish-buff sandy soils on the pediment slope at the north-east margin of Endauand at the south foot of Kituku hill, near Endau village.

Following the completion of the most recent peneplanation in the area it seems thatthin sheets of conglomerate were spread widely over the present and adjacent areas (they havebeen seen by the writer in the areas to the west and north). Sands were also deposited andgently sloping alluvial and colluvial material deposited at the bases of hill masses. Thesedimentary episode seems to have ended in the formation of widespread ferruginous surfacelaterite. The conglomerates must have been deposited under torrential conditions and theclimate generally was probably arid, for any sort of continuous vegetation cover wouldhave prevented widespread deposition.

The age of the beds can only be inferred in a general way from the erosional history ofthe whole of eastern Kenya, for no fossils have been found in them. The beds occur on theend-Tertiary peneplain of Northern Kenya (Dixey 1948, pp. 16-17) and incision by riversinto this surface in other areas is dated roughly as lower Pleistocene on the basis of artifactdiscoveries (op. cit. p. 17). The beds in the present area are regarded as latest Tertiary orearly Pleistocene in age.

5. Alluvial Clays and Silts

Following the deposition of the conglomerates, sands and laterites described above,there was a short period of incision of the drainage around the margins of the hills and along

a suggestion that there is a complete grat‘latitm between ll'iil‘tlniVC rocks and fenites of variouskinds. Owing to the scattered nature ot‘ the exposures and the rapid variation ol‘ rock typesthe geological boundaries in thi\ part of the area are necessarily iCtilLlliHJ.

The l'enites from the northern and north-western margin ot‘ Engamba are notable inlacking aegirine and st ia—amphiboles such as eharaeteri7e almost ttli t‘enites. The develop-ment of turbid and replacive alltali—t‘ttspar at the expense ot" quartz is. howex er. characteristicot‘ l‘eniti/ation law Campbell Smith. l956. pp. 203412).

4. ("t'inglottlt-rates. Sands and Lateritie DepositsThere is indirect etidenee that much ol‘ the featureless plain that exists o\ er most of the

area is underlain by sediments. The extreme scarcity ot' e\posures. even on the sides of theshallow Valleys. and the occurrence ol' tloat pebbles and g ‘tt_\‘ transported soils on some\alle)’ sides suggest that the pencplained surl'ace ot‘ Basement System rocks is orerlain h} athin sedimentar) emer.

lzxposures of conglomerates are most numerous on the sides of the \iatia \t’tlley nearthe crossing of the Sosomd Engtttnba motor—track llere \\'C.ll\'i)>CCt‘.1Cnl€d poorly—sortedconglomerates with quartz and pegmatite pebbles up to four inches in diameter are exposed.\xith a thickness ol‘ up venty feet. Uther e\posures ttnd pebble accumulations werefound [It \a 'ious ' localities. The bngantba Buku motor—track. for examplebelow the north lace ot‘ Engambd runs just to the south ot‘ a low bank on which are abundantloose pebbles. The survey station at 1.. 5t) i‘eet three and a hall‘ miles soutl —cdst of Twambuiis situated on a mound ol‘ quart7 pebbles. Good exposures ot‘ bron n conglomerates de\ oldof bedding occur on the rise to the plain on the south bank the Mumoni ri\'er two miles\a'estAsouth—uest ot’ Msemei \‘xuter—hole Shattered occurrences or” pebble fiottt in quartzosesoils are round atom the sides of the Nzita and \iumoni \LtiiC}S from \lakuka and Katumbias far as Ngtx'aniwa and beyond. Generalh speaking. the etidenee suggests that thin eon—giomerates and sands occur underlying the greater part of the area marked Lh coVered b}reddish brown sandy soil and the elas soils ol‘ the plains.

Boulders ol‘ cellular ironstone and smttll €\}‘\l>tll'CS ot‘ colluvial poorl_\r—sorted grits withironstone 7ones and cuppings occur t‘requentlg. at the margins ot‘ the bills at the letel ot. theplain. The better exposures ure at the base ot [tigtu’nbu hill one mile e trnorth~east ol‘ theeastern summit, \\ here exposures in a stream section SiiO\\ t‘elspar grains in an iron stainedmatrix of sand and silti These beds are at a slightly higher iC\Ci than the heaps of quartzpebbles that occur on the pediment a little t‘ttrther to the north. At the base or the south faceof Kalongola are further grits coloured pale grey. bronn and reddish broom. and cappedh} cellular ironstone ()n the IndauiMakuka motor-track immediately north and north—westof S}'Llll dam there are scattered boulders ot~ cellular ironstone. and similar boulders arecommon near “tilting-ting; statervholei Sheets of loose ironstone nodules are common onbutt and reddish-bull sandy soils on the pediment slope at the north-east margin ot" Endauand at the south that ol‘ Kitttktt hill. near Endau \‘ilzage.

Following the ernnpletitm ot’ the most recent peneplanation in the area it seems thatthin sheets ot'conglomerate were spread widely 0't the present and adjacent ureas tthe}; ha\ ebeen seen by the m ‘ in the at as to the west and north). Sands were also deposited andgently sloping ulltoim and eolEuxial material deposited at the bases of hill masses. Thesedimentary episode seems to lime ended in the formation or u idespt'eud ferruginous surfacelatcrite The conglomerates must httxe been deposited under torrential conditions and theclimate generally “its probably arid. for an} sort ot‘ continuous \egettttion cover wouldiitC preVentcd widespread deposition.

The age or the bed» can onl} be interred in a general way limit the erosional history ofthe \\ hole ot‘ eastern Reina. l‘or no fossils have been found in them. The beds oeeur on theend-Tertiary neneplttin ot‘ Northern lx'enytt tDix’ey 1948. pp. 1677-]?! and incision b} rix'ersinto this surf; "e in other areas is dated roughly tts loner Pleistocene on the basis of artifactdiscoveries top. cit. p. IT). The beds in the present area are regarded as latest ‘l‘ertiary orearly Pleistocene iit u ‘

5. Alluvial Clays and SiltsFollowing the deposition ol‘ the cortglmneratcs. sands and laterites described above.

there uas a short. period 01‘ incision or“ the drainage around the margins ot‘ the hills and along

-

lI

I

,:I

'L~~=

10

"

the courses of the major rivers. The Munyoni-Nziu river system was incised to a depth ofapproximately 200 feet below the surface of the surrounding plain. The early youthful formof this drainage system is very well shown between Ngomano and Makuka. There thenfollowed aggradation and the partial filling of the valleys by level expanses of fluviatile claysand silts. This alluvial sediment is much the same wherever it is seen-it is a brown, slightlygritty, unstratified alluvium with very scarce thin gravel lenses. The present-day streamchannels are locally incised to a shallow depth in this alluvium and are occupied by meander-ing, braided and tapering seasonal streams.

6. Superficial SoilsReddish brown sandy soils are found over the greater part of the plain, and support a

dense growth of thorn scrub. Locally, as at Kamuluyuni and Mulanganga, the soils arebuff or greyish buff and gritty in texture. These are residual soils over syenite and feniterocks.

Along the very shallow seasonal stream channels which occur mostly in the eastern halfof the area, are grey and brown clay soils which merge into the reddish brown sandy soilsof the plains. These soils occur also in very shallow depressions and are due largely to swampyconditions. They are similar to but differ in origin from the brown clay soils found in theflat bottomed larger valleys. These latter soils are developed on the alluvium valley-fill thatoccurs in all the larger valleys, in particular that of the Nziu.

Irregular areas of black-cotton soil are found on the flat plains at several localities, thelargest such occurrence being the area south of Msemei and Mulingwa water-holes. These

. soils are characterized by an almost complete lack of thorn scrub and by deep drying cracks.They may represent the remnants of a more widespread sheet of such soil formed during~'long period of greater rainfall.

A further broad group of soils distinguished locally are the transported or valley slopesoils. These are yellowish sands and yellowish brown soils, which sometimes contain ironstonenodules and pebbles derived from conglomerates. They are found on the sides of the majorvalleys and on the gentle pediment slopes at the margins of hills. They are formed largelyof material derived from the sheet erosion of peneplain deposits (the conglomerates, sandsand laterites described above).

In the vicinity of Kathua, Endau village and Kwandana the soils are usually darkhumus-rich types formed in the more heavily forested area south-west of Endau, an areawith a distinctive and more luxurious vegetation on account of the relatively higher rainfallit receives. The soils on the Endau and Engamba hills are similar to these, being dark brownclay-rich types characteristic of areas covered by dense vegetation. On some parts of Endau,however, where gully erosion in old cultivated areas has exposed the subsoil it is seen to bepale reddish buff in colour, and may have a bauxitic composition.

V-STRUCTURE

The exposures of Basement System rocks in the area are inadequate to allow a structuralsynthesis to be made. Opposed dips in the region of Endau village are suggestive of a broadanticline trending north-west-south-east and plunging to the south-east. The occurrenceof vertical beds striking north-north-west on the left bank of the Nziu river west of Kamulu-yuni suggests that local fold-axes parallel this direction. The disposition of the foliationin the area generally is not incompatible with north-south or north-west-south-east-trending fold axes, such as have been postulated in the area to the west (Sanders, 1954, pp.34-42).

Only three lineations were measured in the area, and these trend approximately north-east-south-west. Lack of exposures prevents their interpretation.

A curving of the strike of the quartzo-felspathic granulites in the Siobiliwa-Syu areasuggests a wedging action by the Endau intrusive. There is no evidence for such an effect,however, in the vicinity of Endau village.

Structures within the quartz-syenite intrusions are limited to jointing and small narrowshear-zones. The latter are found at the northernmost extremity of the Endau syenite, in theMiosya river, and on the north face of Engamba. In each case the shears are orientated

-

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I

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'L~~=

10

"

the courses of the major rivers. The Munyoni-Nziu river system was incised to a depth ofapproximately 200 feet below the surface of the surrounding plain. The early youthful formof this drainage system is very well shown between Ngomano and Makuka. There thenfollowed aggradation and the partial filling of the valleys by level expanses of fluviatile claysand silts. This alluvial sediment is much the same wherever it is seen-it is a brown, slightlygritty, unstratified alluvium with very scarce thin gravel lenses. The present-day streamchannels are locally incised to a shallow depth in this alluvium and are occupied by meander-ing, braided and tapering seasonal streams.

6. Superficial SoilsReddish brown sandy soils are found over the greater part of the plain, and support a

dense growth of thorn scrub. Locally, as at Kamuluyuni and Mulanganga, the soils arebuff or greyish buff and gritty in texture. These are residual soils over syenite and feniterocks.

Along the very shallow seasonal stream channels which occur mostly in the eastern halfof the area, are grey and brown clay soils which merge into the reddish brown sandy soilsof the plains. These soils occur also in very shallow depressions and are due largely to swampyconditions. They are similar to but differ in origin from the brown clay soils found in theflat bottomed larger valleys. These latter soils are developed on the alluvium valley-fill thatoccurs in all the larger valleys, in particular that of the Nziu.

Irregular areas of black-cotton soil are found on the flat plains at several localities, thelargest such occurrence being the area south of Msemei and Mulingwa water-holes. These

. soils are characterized by an almost complete lack of thorn scrub and by deep drying cracks.They may represent the remnants of a more widespread sheet of such soil formed during~'long period of greater rainfall.

A further broad group of soils distinguished locally are the transported or valley slopesoils. These are yellowish sands and yellowish brown soils, which sometimes contain ironstonenodules and pebbles derived from conglomerates. They are found on the sides of the majorvalleys and on the gentle pediment slopes at the margins of hills. They are formed largelyof material derived from the sheet erosion of peneplain deposits (the conglomerates, sandsand laterites described above).

In the vicinity of Kathua, Endau village and Kwandana the soils are usually darkhumus-rich types formed in the more heavily forested area south-west of Endau, an areawith a distinctive and more luxurious vegetation on account of the relatively higher rainfallit receives. The soils on the Endau and Engamba hills are similar to these, being dark brownclay-rich types characteristic of areas covered by dense vegetation. On some parts of Endau,however, where gully erosion in old cultivated areas has exposed the subsoil it is seen to bepale reddish buff in colour, and may have a bauxitic composition.

V-STRUCTURE

The exposures of Basement System rocks in the area are inadequate to allow a structuralsynthesis to be made. Opposed dips in the region of Endau village are suggestive of a broadanticline trending north-west-south-east and plunging to the south-east. The occurrenceof vertical beds striking north-north-west on the left bank of the Nziu river west of Kamulu-yuni suggests that local fold-axes parallel this direction. The disposition of the foliationin the area generally is not incompatible with north-south or north-west-south-east-trending fold axes, such as have been postulated in the area to the west (Sanders, 1954, pp.34-42).

Only three lineations were measured in the area, and these trend approximately north-east-south-west. Lack of exposures prevents their interpretation.

A curving of the strike of the quartzo-felspathic granulites in the Siobiliwa-Syu areasuggests a wedging action by the Endau intrusive. There is no evidence for such an effect,however, in the vicinity of Endau village.

Structures within the quartz-syenite intrusions are limited to jointing and small narrowshear-zones. The latter are found at the northernmost extremity of the Endau syenite, in theMiosya river, and on the north face of Engamba. In each case the shears are orientated

111C courscg L11'111c 11111101' 1'11.L‘1‘\:. 1'11L'1 1‘-.‘1L 11.111'1111-V/111 1'11L‘1';1pprox1111z1101}1 2(1'L111L‘L11. 11L11L11111111L 1:11‘1;1L1L'1 1:111 1.11L \ .11:111 11113 druinugc 53.510111 1\ \L1_\. L\L—'1i 51111.11 11LI1.l‘L'111111.\1r;1L1aggrudzmon L1 111; 1,1..1L11111 1: 11; 1111111.: \.1111(151115. This 111111\;11‘1 .5L‘1L111111C111 15111L1L'11111L 5.11111; 1‘ 1s <L‘L‘L1—1t19111‘:‘L1\111.sl'1§;1111}'gritty unstratir‘rcd 1111111111111 112111 \cr'jv sL‘L11‘Lfc 111111 L11'111L11 -1155 The 111'L‘sL11111L1-L'1y 51110111111Ch111'11t‘1‘3‘ ElI'L‘ 1L1'L 1111' 111C15L11 10 1; >h1111111111 11:11.1111 1'111115111111111.11'1L1:1L11L:1L‘1LL1L'111.‘11L13131'111121111L‘1Crv1115;111‘121L16112111L1 1:111L‘1'2111; «131181111 5111:11111»

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. LLL‘UI‘ 111115.1\11.1111;11‘1L' \31'1'5111111111 sL‘.15L'1:1'L1.1 >11‘L11.01' the area. are {FL} and 1)1‘L.111\‘1‘= L11) 91.1111011111: 1111111151. 'l‘hcsc $1'111\.11L'L'11:‘L11.1.1i111L1 .11L1 11': via: 1111'gc131 to 5111411111)conditions. T21C}' .11‘L‘ 5111111111111 11111 12111.: 1.1. 1511111111 111.121‘ 1111.: 1.1111111 L11.1;. «1115 111111111 in The11:11 hunnmcd larger 1.1111311}. ‘111L‘5L‘ 11.1.11L'11' 1.1111. . 1.1.211311111LL: L111 1111‘ .111L1111'L1111 \1111L15~1:11 1.11:1!occurs 111 1.111 1116 1111‘;L1' \1;11EL1_\'15_ 111 11.11'1'1L1111111' 121:1: 1.11'1‘11L'1 .\/.'11.1.

1

11'1'L‘gL11'L11'111'L'LLS '.11'21122‘\L‘2\‘L'L.‘1:111‘111 \1 L‘1‘L1L.:1L" 1111 1111. 11.11 1..111.'1\ .11 .L'.1 L111 '1.LL‘1.11.111L's 111C1111‘gcstsuc111.1:L‘1L11‘1‘C11L'11." 11L1..11; 1.111.- 1...'L.1 '1 1.1131 1.5 \1<1;111L'-1 .11111 1\‘1L11111~'r 11 1111151.1115111'L' L11111'11L‘1c1‘izL'L111 .1111..1111L1..\1. L1L1:111,'1L1;.1;.1L'1LL1 :11131‘1‘ \k'1‘1.‘1.‘1 .1110. '11.) d1.Tl‘lt‘}; 111.1} TCDE‘Cx‘L‘I‘Il 121L' 1'L11'1111.111{; 1'1: ":1. 11mg 11(11'11111‘ 111' greater 11111111121.

1L’.~l‘:01L‘>. 1ThL‘SC, .1111131113; cracks.

‘.1.112L‘\1‘1L".:L1 17"1‘L‘L‘1 11 K.1L"11 \1111 i‘uynk’ml dupng

13. 1111111101 broad am:111 L11" 5211’ I 1.."1L'1‘111} 1.11L' 1111.1 11'1121x11111'IL1L1 1.11' 1-.;111L‘_\ alum"SOUS. ThL‘SC (111‘ ‘ c10111521s'111dx :11“; 1:11.11 \11 111111.111 x1011).“(112111.121\1j1111g11j11‘ex gmlu m ir'nnx'tonc111.11.1111L15111111 pbiL'» L1L1‘11L'L'1110111L‘1j111g11'1.1:'.1LL'\.. 111L11.:11'5111111L1L1111111L.s1d1L> 111 1111: 1111.111):\‘L'LHCVS 1111d111111161;L111L1L‘1.1L1L1‘111'1L1111511111.15 1.11111L‘ 11:11::11\ L11 1 :«. i11L1\11L1L1111L1L111‘11Ll\1‘11 1111.11L1‘1111L'1L‘1'11Ld 1111111 1111c x11LL1 {1'11‘1112 '1 11 :1L1.1L11‘.1 1.111 L1L11L'1x115 111'1L' L12.111;111:1 :'.11L3.51.'111L1'L‘{111(1].11L111L'> LiLsL'1ibL'1L1 1.1100121.

1

In thL‘ \1Cinity 01‘ K151111311. h11L1L111 111111;.- 1111L1 K113111411; ’1‘1L‘ $1i‘111x '.1.1'L‘ 11<L1L1EI} darkhUKTILi\-1'1L‘h mpcs 11.11‘111LL. 1.11 1.11." 1111.11L" '11L'1.1.1.11} 1‘1'11'L'1.1L"1.1 .1:'L".1 sL111‘111-1..L\1 1111 :1d1111 1.1.11. 11:13.11.111111 11(113111'1L‘111L‘ {111d11111113111\1:1‘1L1‘11< \1:1;L‘1:;111.'11‘1 1:111 1.1L‘L‘1é1111111-1‘11.1111L111'LL1\'1111;11L:r 11111111111111'CL‘C1\L‘S. The 3011911111112 1.11L11.11.1.111L1 F 7 11111111 111111:111'1:\1:1‘11.1"11'1111LL1L". 1min: L111' k 1311.111 11C111y—1‘1L'E1typcs L11111'11L'1L‘1‘1311L' L15 11111.15 L'1'1‘1L'1L1L1 '11) Liam: c1111 1.11‘. (.‘11‘. L111:11L'111.111\, 11. 11111111;hmvcwr. “111.1111 gu11)‘ C1'(‘\'1'CI'1 3111 mid LL;111\1.11L'1L1 1.10.13 111.1\ L‘\.1‘11.‘\‘L‘1 1'1L \11. $1.11 1 1' 1x <L'L'1‘. .11 hL'11:11:“ reddish h1111'1z1L11‘11L1111‘. .1.111L1 111:1; 11.1111.L1 1.: 1 ;:11\111L' L111L1'1‘111152111'111.

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11

approximately north-south and are inclined at steep angles. The orientation of some majorjoints is shown on the map. The majority trend either north-north-east or north-north-west.A strongly marked set of joints on Kandelongwe trends north-west. Again the data areinadequate, but are compatible with an east-west stress system.

VI-MINERAL DEPOSITS1. General

No economic minerals were discovered in the Endau area, and none have been dis-covered previously. A search was made for possible mineral occurrences at the margins ofthe syenite intrusives, but without success. No radioactive minerals or rocks were discovered.The alkaline nature of the intrusives and the absence on the surface of basic members of thesuite suggest that a mineralization connected with the intrusives is unlikely.

4

: (

11..

,)

2. WaterAlmost all the work carried out by government agencies hitherto has been devoted to the

improvement of water-supplies. A small concrete dam has been constructed below theKwamutia spring and from this a one-inch-bore pipe carries water to Endau village, afterhaving passed through four break-pressure tanks. This water-supply is generally exhaustedby mid-morning and is inadequate for the needs of the village. The water-level frequentlyfalls close to the level of the intake pipe in the headworks, and any fall-off in spring flow,which is in any case a mere trickle, would result in a temporary cut-off of supplies. A partialremedy for this state of affairs would be to build a small intake dam at the Mukuyuni springnearby and to connect this by a pipe-line to the first break-pressure tank. An increase in thebore of the pipe-line would be needed to ensure a more adequate flow.

Two boreholes have been drilled near Endau village, numbers C.1300 and C.l543, thepositions of which are shown on the map. The first of these boreholes was drilled to a depthof 320 feet and struck water at a depth of 38 feet, rising to 27 feet. The yield is 8,040 gallonsper 24 hours. The borehole log is as follows:-

BOREHOLE C.1300Log ft.0- 26 Black sandy soil

26- 43 Granitic gneiss with hornblende43-116 Quartz-biotite gneiss

116-119 Felspar pegmatite119-300 Quartz-biotite gneiss300-320 Grey talcose rock

Partial analysis of water from the borehole indicated:-

",

l

'I

I

parts per 100,000Cl .. .. .. . . .. . . .. 1,500NaCI . . . . . . . . . . . . 2,600

This borehole therefore had a low yield and the water was too saline for human or animalconsumption.

Borehole C.1546 was drilled a little further east to a depth of 200 feet without reachingwater. The conclusions reached as a result of this drilling were that the prospects for succesfulboreholes are slight, on account of the salinity of the ground-water.

The greater part of the water for domestic purposes in the Endau-Kalungu vicinity isobtained from the beds of the rivers. Perennial water is obtainable at Kwandana, Kalunguand Katumbi, but further downstream in ihe Munyoni river the conditions are unfavourableand no wells are dug. No wells were observed in the Nziu river, which appears to be un-favourable. A group of wells was found in the Miosya river at Malalani. Numbers of smallwells or rock pools occur below the north face of Engamba and at the foot of Kinani rock.These are seasonal and support a number of cattle after the rains. Further wells occur atKamuluyuni, but seem to be disused.

Dams have been constructed at Syu and Makuka; the latter is more successful andprovides a perennial water-supply from wells dug in the river bed just up-stream from thedam. The principal dry weather watering places are the Katumbi, Kalungu and Kwandanewells and the Endau reservoir of piped water. Further north the Makuka dam and the

11

approximately north-south and are inclined at steep angles. The orientation of some majorjoints is shown on the map. The majority trend either north-north-east or north-north-west.A strongly marked set of joints on Kandelongwe trends north-west. Again the data areinadequate, but are compatible with an east-west stress system.

VI-MINERAL DEPOSITS1. General

No economic minerals were discovered in the Endau area, and none have been dis-covered previously. A search was made for possible mineral occurrences at the margins ofthe syenite intrusives, but without success. No radioactive minerals or rocks were discovered.The alkaline nature of the intrusives and the absence on the surface of basic members of thesuite suggest that a mineralization connected with the intrusives is unlikely.

4

: (

11..

,)

2. WaterAlmost all the work carried out by government agencies hitherto has been devoted to the

improvement of water-supplies. A small concrete dam has been constructed below theKwamutia spring and from this a one-inch-bore pipe carries water to Endau village, afterhaving passed through four break-pressure tanks. This water-supply is generally exhaustedby mid-morning and is inadequate for the needs of the village. The water-level frequentlyfalls close to the level of the intake pipe in the headworks, and any fall-off in spring flow,which is in any case a mere trickle, would result in a temporary cut-off of supplies. A partialremedy for this state of affairs would be to build a small intake dam at the Mukuyuni springnearby and to connect this by a pipe-line to the first break-pressure tank. An increase in thebore of the pipe-line would be needed to ensure a more adequate flow.

Two boreholes have been drilled near Endau village, numbers C.1300 and C.l543, thepositions of which are shown on the map. The first of these boreholes was drilled to a depthof 320 feet and struck water at a depth of 38 feet, rising to 27 feet. The yield is 8,040 gallonsper 24 hours. The borehole log is as follows:-

BOREHOLE C.1300Log ft.0- 26 Black sandy soil

26- 43 Granitic gneiss with hornblende43-116 Quartz-biotite gneiss

116-119 Felspar pegmatite119-300 Quartz-biotite gneiss300-320 Grey talcose rock

Partial analysis of water from the borehole indicated:-

",

l

'I

I

parts per 100,000Cl .. .. .. . . .. . . .. 1,500NaCI . . . . . . . . . . . . 2,600

This borehole therefore had a low yield and the water was too saline for human or animalconsumption.

Borehole C.1546 was drilled a little further east to a depth of 200 feet without reachingwater. The conclusions reached as a result of this drilling were that the prospects for succesfulboreholes are slight, on account of the salinity of the ground-water.

The greater part of the water for domestic purposes in the Endau-Kalungu vicinity isobtained from the beds of the rivers. Perennial water is obtainable at Kwandana, Kalunguand Katumbi, but further downstream in ihe Munyoni river the conditions are unfavourableand no wells are dug. No wells were observed in the Nziu river, which appears to be un-favourable. A group of wells was found in the Miosya river at Malalani. Numbers of smallwells or rock pools occur below the north face of Engamba and at the foot of Kinani rock.These are seasonal and support a number of cattle after the rains. Further wells occur atKamuluyuni, but seem to be disused.

Dams have been constructed at Syu and Makuka; the latter is more successful andprovides a perennial water-supply from wells dug in the river bed just up-stream from thedam. The principal dry weather watering places are the Katumbi, Kalungu and Kwandanewells and the Endau reservoir of piped water. Further north the Makuka dam and the

approximuucl) HUF'Ll‘l-Sollll‘l 111111 Lll'L" 111L3111L'Ll .11 steep Jingles. 'l'l1L' L11'1'13111'111l1111 111' some majorjoints is slum 11 L111 111:- 111.111. The 1'11;1._lL'1=.'l1_5 ll'C‘llLl 'L'ltl1c1' 11111'1l1 —11L11'1l1-L"11.5? 01' l]0l'lh-IlOl'[h—\~\ e51.A. strongly marked 5e: 111' jL111115' 1:111 KL‘111L'1L‘lL111L1'11L' 11'L'11L1i5: :1111'151-11Inadequule. but 1111? cc .1111lil1lL' 'L\11l1 :111 C115 1— 1.10.51 511'L'5'5 51.511311.

\gnln the clam 2110

\‘l—MINERAL DEPOSITSI. General

No CL'Or1L'1111iL' 111111L'1';:l5‘ \1L‘1'c L'll5L‘L'11c1'L'Ll 111 the Enduu 111611. and none have been 1115-LIO\€I‘€(l previously .=\ 561:1'L'l1 11:15 111:1dL‘. l'm 11L1551E1lL' 111111c1'L1l occurrences 211 the margum (11‘t 55011116 1'1111'1151'1L'5'. l1L11 11.11l111111 51,1L'L'L'55. l\1.11'11dl1111:=.11c111111L'1'11l5' L1r'1'L'1L‘lL5 \1'L'1'L' Lli5iCL11'L‘1'cd.Tl1L'L1lk'L11111L‘ 11111111'L' L1l'1l1'L' 1111111525 L5 11ml ‘1l‘1L'1'1l,15'L'1'1L'1: 1121 1l1L' 5111'1'11L'L' L1l' l1:.51L" 111311111615 L1f1l1L'5Lz11L' suggest 1l1L1I ‘1': 111111L':';1'l17;1,1EL111 L'L11111CL'1L'Ll \111l1 :l1L' 1:111'11525Q5 1'5 11nl1lLL'lj1.

\Vatcr.'\]l11C'S[ .111 the 11ml L"11:'1'1L'Ll01.11l'yg1,1'1L'1'11111L‘11l.1gL'11L'1Lé5l11§l1c1111l1115l1L'L'11'LlL'1L1tL'L'imlhc

1111111'1'11'61116111 1,1l' 1.1.111L'" 511',111llL5 \ 511111ll L'L'111L‘1'L'1L' Ll'L1111 l1115 been L‘L'111511'11L'1L'Ll below theK15;1111uti:1 spring :111Ll l'.1,'1.'11 11115 .1 11115111151114 L' A111 L" L".11‘1'1L'5 under N E1 1L'l'.111 1'ill'1137L'_;1l'tL'1'llmilm passedIl111'111ul1l'11'111' l,11‘L‘:L1lL-1,“11L‘1551:1'L' ‘1: 1l55. T'115‘ 11111L1—5LI1111l\115' ga‘I'Llllx L‘tsLll'Lll.1\ 111ld-11111r11iz1g and 15 11‘1'. LlL' 11:1111L' l'L11 11'1L' 11LL"Ll5 11.1 H1: \1ll11g‘. ll1'L" 1'1;11L'1'-lc1'cl l1‘cqucnlbl11l|s C103: l1) ll1L' IL'xL‘l 1:11 1l1c 1111'.c 1111,1Li11t11L'E1L'L1Ll11L11lL1' 1d :11\ ml] MT in 15111111}; flow.\1l1i'Ll115‘ 111 '111\ L115: ;. 111L1L' 111LlL'lL‘. 1511'L1lL1 11:51: l1 111 1 1L1111L11' .'1.1\ LL1l-L,1ll111511.111l105. A 112111111]1'L‘111edvl101' this 1:111;1'11z1ll':111'5'111,1ul'dl131L1'11111lLl:15:1‘ 111111lLLL1L1:1,;111l1L \111k111111115111'1ngllLlll'b) u111l11,1L'L'1.11'1cL"11l115 l1) :1. 1,1111c-l1s1L1L11l1cl11'51 .1 L'11lL»1,11'L-:.511:L': funk. .\1'1 i11L'1'c115L'i11tE1L'bore 'L'1l‘1l1c 1111,1L'»l:nc would he llC‘L'LlL‘Ll 11,1 'L'1‘.5'111c '11 1111.1

l LLl 11L'111' l..1 '2 11.1111 'l'nL'l

1L" '..1.L"L11:;11L' ll1,'1'.'1.

Two 111'1r'el111lL'5' l1;1\c l1L'L'11 L'l1'1 m '11ll'nL“ :1111'11l1L15 ( 1301") and ('.l5~1.‘1. Il1L'1111511111115 01' 1‘. l11L‘l1 L11'L' 5l1L1'L' :1 L1111l 5l1‘1:'ll1L",5L l1111'L'.1L1lL‘.5‘ 11:15 Lll‘lllL‘Ll To '11 depthL'1l‘32l)I'LL-11111Ll511'uLlL \5'11'L'1'11‘.:1Ll.':11'1l'1115.1151'L‘L'3 115 nu 111 ll1€1LEclLl15 3.040gull1'1n15pcr 2 lIL'z'111 5 Tl1L b111' 'l111lc'111' 15 :15 l1,1ll1,'1'1\:5':7

R1,11{L'11111,1 (1711111[.111 1‘!

U 311 Rl,11L"1L 5111111} mil:67 3 (11".11'1111L' unclss \1l1l1 l11'11'11l1l'L'11LlL'

‘1~|l(,1 ()L1L1114-l1111lilL' g11c155'116 i 1‘) FL [.511'11 1cg111L1ai1L=11971301) Qu1‘117-l,11L1111L‘ {4:12:55710073120 (he) I‘LllLL15‘L' 1'L1L‘l-L

P1111111] 1111'L'1l15i5 Ql' 11".1IL‘1' l'r1'1111 ll1L' l,11,11‘L'l1L1lL' 111L11L'L'11L‘Ll:111111.11- 1117‘ 100.0110

Cl .. .. .. . . .. . 1.501,)NdCl . . . . . . . . . . 2.1100

This borehole ll1L'1'cl'L11'L‘ l1:1Ll a l111'. _\1t Ll the 11".11L'1' 11:15 11,111 511li11c 1111' 11111111111 (,11' 11111111111L‘L1115L11111111011.

BL1'cl1olL ( l5-l6 11115 L'l1'illL'Ll :1 Mil: l'11:'1l1L'1' c1155 11,1 '11 Li 11l1 11l' 300 feet 1110111111 reachingr1.5111161: Tl1L' LL111LlL151111151'L'11L'E1L'Ll:15111'L",'51:ll1.1l'1l115 drilling'L'-.L"1'L"1l1111 ll1c 111'L1511L‘L‘15l'ol'sncucsl'ull1L'11'L‘l1L1lL'5 :11‘L' slight. L111 :1L‘L'L111n1 L15 1'11: 5:1l11111} 1'1511‘1: g1'1111r1Ll-11111L'1'.

The great-er 111111 111' 1l1L- 11.11L'1' lo.‘ Ll1.'1111c.5tiL" 11111'111'15'L'5 111 UN: E11L'lL11;-l\"1lung11 \1L‘i11ity 1.5‘obtalncd from ll1L' hub 01' 1l1c 1'1'1L'1'5'. PL'r'L'1 111111 ."L11c1' l5 11l1l;1i11:1l,1lc L11 l\'1-.;111.'Ll 111:1 KalunguundKulumbl. l1L1l l'111'll1L‘1'd111'111511'L1'Ll11'1 111 We 11.111.111.11 1'11L1' ll1L LL111Ll'1.1'L1115 111C L111l.1\11u1'.1bl'c1111Lln11 \5L'l‘1511z‘c (lug. T\'1,1\\L'li5 11cm L'1l1.L':'1.LLl 111 1l1L' \‘7l1; ll\1‘;l'. 11‘111L'l1 :11111L;11510 b1: L111-1111 ourublL'. .’\ group 111' \1Lll5 11.15 found 111 1216 .‘\1l1'15'1".1 1'11L'1'111 l\l'.12'1'.l'1111i. \1‘11111l1L11'5 L1l'5111z1llwells 01‘ rock 11L1L1l5 ClCCLll' l.1L"l11\1 lhl.‘ 111,11'1l1 face of E11511111l1:1 and :11 1h: 1111M 111' Kinuni rock.Tl1L'5L' 1111: seasonal and 51111111111 11 llLlll'll‘l‘L‘l' 1'1l' L1111lL' 1111131 1l1c :'.1i:15. 1".1'11l1c: 115clls occur :11Kumuluyuni. 1.13.11 5x111 11,1 l.1L‘ L‘115L15L'Ll.

13.1.1115 l1:1\L' l1cc1tL‘1111511'11L1Ld 111 S111 and MnlLlalz the lunar 1.5 man: successful and'111‘L11'lde5 L1 11e"C11‘11:1l .11'L1LL1'—5'L111;,1l_.' l'1'11‘1111 '11L'll’L5‘ @1n 111 'Ll'1L' 2'1\L‘1’ E1C1L§_EL1.51 u11-511'c11111 111.1111 thedam. The 111'1116111L1l Llr\ 111L.1ll1L;'11.1:L'1'E11g11l11L'L'5;‘11'L' [he KLllnl‘J‘w. Knlunflu 'L‘aml K11'L'111L12111e\VL‘llS 11nd the 'E1'11l1;1 :L5L':'1.1111 111' 11133911 '1'1'111L'11: l7111'1l1L'1' 111'11'll'. ll'L' MdknlL'u dam and the

12

Mala1ani wells provide perennial water. In the eastern two-thirds of the area there is noperennial water-supply.

Numerous seasonal water-holes occur throughout the area, some of them, such asEyuku, Mutanda and Yanzeu, being large pans over 100 yards wide. None of them containwater all the year round, except possibly in years of exceptional rains. It is these water-holesthat provide for the cattle that are driven into the Eastern Crown Lands after the rains.

During 1952-53 a number of hand-auger boreholes were drilled by the African LandDevelopment organization in or near river-beds in the area. The approximate positions ofthe bore-holes are shown on the geological map. The results of this drilling were as follows:-

The tabulation shows that perched water exists in the alluvials of the Nziu and Matiarivers, and geological circumstances indicate that water could probably be found in theNziu river alluvium at many places along its course. No test pumping was carried out at theborings, and should a further: investigation be carried out such pumping would indicatewhether well-sinking is justified.

Apart from the possibility of establishing a chain of wells along the major rivers, theonly other possibilities for improving the water-supply in the area are the construction ofsmall dams and the excavation of water-holes to form tanks.

VII-REFERENCES

Champion, A. M., 1912.-"The Thowa River." Jour. E.A. Nat. Hist. Soc., vol. Ill, pp. 13-20.

Crowther, A. F., 1957.-"Geology of the Mwingi Area, North Kitui." Rept. No. 38, Geol.Surv. Kenya.

Dixey, F., 1948.-"Geology of Northern Kenya." Rept. No. 15, Geol. Surv. Kenya., W. Campbell Smith and C. B. Bisset, 1955.-"The Chilwa Series of Southern

Nyasaland." Bull. No.5, Geol. Surv. Nyasaland.

Johanssen, A., 1941, 1937.-"A Descriptive Petrography of the Igneous Rocks." Vols.II and III.

Saggerson, E. P., 1957.-"Geology of the South Kitui Area." Rept. No. 37, Geol. Surv.Kenya.

Sanders, L. D., 1954.-"Geology of the Kitui Area." Rept. No. 30, Geol. Surv. Kenya.

Smith, W. Campbell, 1956.-"A Review of some Problems of African Carbonatites."Quart. Jour. Geol. Soc., vol. cxii, pp. 189-220.

Stringer, K. V., D. N. Holt and A. W. Groves, 1956.-"The Chambe Plateau Ring Complexof Ny asalan d." Col. Geol. and Min. Res., vol. 6, No.1, pp. 3-18.

G.P.K.485-800-2/61

,b~-

Borehole Location Water Water rest TotalNo. struck level depth--

(feet) (feet) (feet)6 Kalikubu River .. .. .. - - 687 Kalikubu River .. .. .. - - 508 Ngomano (Nziu river) .. .. - - 809 Ngomano (Nziu river) .. .. 58 53 62

10 Matia river .. .. .. .. abandoned on striking gravel11 Matia river .. .. .. .. - I - 80t12 Kalamba (Matia river) .. .. 57 56 6013 Kalamba (Matia river) .. .. - - 6214

IKalamba (Matia river).. .. - - 25

12

Mala1ani wells provide perennial water. In the eastern two-thirds of the area there is noperennial water-supply.

Numerous seasonal water-holes occur throughout the area, some of them, such asEyuku, Mutanda and Yanzeu, being large pans over 100 yards wide. None of them containwater all the year round, except possibly in years of exceptional rains. It is these water-holesthat provide for the cattle that are driven into the Eastern Crown Lands after the rains.

During 1952-53 a number of hand-auger boreholes were drilled by the African LandDevelopment organization in or near river-beds in the area. The approximate positions ofthe bore-holes are shown on the geological map. The results of this drilling were as follows:-

The tabulation shows that perched water exists in the alluvials of the Nziu and Matiarivers, and geological circumstances indicate that water could probably be found in theNziu river alluvium at many places along its course. No test pumping was carried out at theborings, and should a further: investigation be carried out such pumping would indicatewhether well-sinking is justified.

Apart from the possibility of establishing a chain of wells along the major rivers, theonly other possibilities for improving the water-supply in the area are the construction ofsmall dams and the excavation of water-holes to form tanks.

VII-REFERENCES

Champion, A. M., 1912.-"The Thowa River." Jour. E.A. Nat. Hist. Soc., vol. Ill, pp. 13-20.

Crowther, A. F., 1957.-"Geology of the Mwingi Area, North Kitui." Rept. No. 38, Geol.Surv. Kenya.

Dixey, F., 1948.-"Geology of Northern Kenya." Rept. No. 15, Geol. Surv. Kenya., W. Campbell Smith and C. B. Bisset, 1955.-"The Chilwa Series of Southern

Nyasaland." Bull. No.5, Geol. Surv. Nyasaland.

Johanssen, A., 1941, 1937.-"A Descriptive Petrography of the Igneous Rocks." Vols.II and III.

Saggerson, E. P., 1957.-"Geology of the South Kitui Area." Rept. No. 37, Geol. Surv.Kenya.

Sanders, L. D., 1954.-"Geology of the Kitui Area." Rept. No. 30, Geol. Surv. Kenya.

Smith, W. Campbell, 1956.-"A Review of some Problems of African Carbonatites."Quart. Jour. Geol. Soc., vol. cxii, pp. 189-220.

Stringer, K. V., D. N. Holt and A. W. Groves, 1956.-"The Chambe Plateau Ring Complexof Ny asalan d." Col. Geol. and Min. Res., vol. 6, No.1, pp. 3-18.

G.P.K.485-800-2/61

,b~-

Borehole Location Water Water rest TotalNo. struck level depth--

(feet) (feet) (feet)6 Kalikubu River .. .. .. - - 687 Kalikubu River .. .. .. - - 508 Ngomano (Nziu river) .. .. - - 809 Ngomano (Nziu river) .. .. 58 53 62

10 Matia river .. .. .. .. abandoned on striking gravel11 Matia river .. .. .. .. - I - 80t12 Kalamba (Matia river) .. .. 57 56 6013 Kalamba (Matia river) .. .. - - 6214

IKalamba (Matia river).. .. - - 25

M'ttlalttni wells prm‘ide nerenniul Miter. ln the eastern tun—think ut' the area there is noperennial water-supply.

Numerous seusonul wuter—holcs OCCLH‘ tl‘tt'Utlgl‘iOtlt the Lll‘CLl. MVIHC ot' them. such asFyuku. .Vlutau'tdt‘t untl ‘r'tin7et:. being huge puns met" ltltl 1. nuts \\l(l‘C.. None of them containwater all the year round. except possibly in wars ol‘ exceptional ruins. It is these water—holesthat hrm itle tor the eztttlc that are tli'ixen into the ELtSlCl'Zl ("min n hands. after the ruins.

During l95 —53 a number at hand—auger boreholes were drilled by the African luntlDevelopment {\l‘glll'll7illl0n in or tL'tl‘ 1'l‘.€l'-lWCtlS in the urea. lhe ttpnrmimeite positions oi"the bore—holes are Show n on the geologieul map. The t‘c>tllt\‘ ot'this drilling \xct'e its follows :7

Borehole l.tie;ttinn \\ tttei‘ Waiter rest TotalNo. ' struek lexel depth

l fut-L'fl (lye!) l fi‘t’fl(f1 Kaililtuhu River .. .. ,. 7 77 68’7 Knilkubu River . . .. 7 , 50.\‘ Ngomttno tl\ziu l'l\i‘l'l . . 7 St.)S) \lgomtmo (N7it1 rhet‘i , . SN 53 (:2

ll) N‘ltttit’t I‘EVCT‘ . V . V . . . nbendonet’l on striking gi‘tnell l \l'dll'd l‘l\CI' V . V . . . 7 7 507';ll Kitllll‘l‘lbtl (\‘littin met) V . . . 57 5b ()0l3 Kulnntbzi (‘V‘l‘dllil fiver) . . . 7 777 (12l4 lxttltunhu (\“lgtizz titer] .. ,. 7 7 7 35.

The tubulution shows that hei‘eheu‘ nutter C\i>t,< in the :illtniuls of the .\‘/iu untl \=l;tti:irivers. and geological eireuntntunees indicate that WHICI' could. probably be found in theN/iu l‘l\'c‘t'L1llll\'llll‘ll at many places along its course. \lo te<t pumping was carried out git thebot'ings. and should u further intestigtttion he etir‘i‘ietl out \uch pumping would indicate:whether \\'ell7sittkiiig is justified.

Apart From the DOSSll)lll[} «it eunblixhing Ll ehuin ol‘ nellx‘ along the major rivers. theonly other po»ihilities tor imprinting the nutcr-stmfly in the uren we the construction 01‘small tlunis untl the exennitiori ot‘ \xiatei‘7holcs to form tunltx.

\ II7RICI<‘ICRF\( ESChmnpion. A. M” l9l2.7"’l'he 'l‘hmm Rixei‘." Jilin: EA. Ant Hm, Sim. Vol. 11L PP- [3731

Crowthe1‘..=\. F. l957.7"Ge(ilt'>g_\ til the Mningi .»\i't':.t. \t’ti‘th Kitui.” Rept. .\ti. 3&(71901,Surv. Kenya

Diwy. F_V [94SV7"Geolog}' tii‘Northei‘n Remit.” Rent, No. l5. ('ietil. Surt‘. Remit.7 77 77 77 7 V \\'. (funiphell Smith t: id C, B. BissetV 1955.7”The Cl]ll\\;l Sei‘im of Southern

Ny‘nsuluntl." Bull. No. 5. (lL‘t‘l. Sim, \ljtusttluntl.Johanssen. A, Ill—ll. 193T. ‘ Des‘et‘ihtite Petrogi‘upli} «‘t‘ the igneous Rocky" \r’o]g_

ll and Ill.

Suggerson. E. l’.. 195177 "('ietilnui.‘ ot' the Santa Rizui Area.” Rem. No. 37. (ieol. Sun.Kenna,

Sanders. L. D,. 1954.7“Cieologt ol‘ the Kitui Men.” Rent. No. 30. (JCLll. Sen. Kenya.Smith. W. Campbell. 1956 '-\ Rmiew at some l’:‘t‘tl‘lCEtt\‘ ol' e\t'rie;tn ("urhontttites."

Quart, Jam: Gt'ul. Stun, \t’il. exii. gm. IN) 320.

Stringer. K. VI. D. .\. Holt (and A. W. (ll‘U'wCL l956.—"The ("humbe Plitteuu Ring Complexot" V5’115zilztml.” (at. Gail. Lind um. Rim. to]. n. \h 1. mi. 3718’.

G,P.K. 495—suu—f‘ia: