TasNat 1925 No1 Vol2 WholeIssue

7/28/2019 TasNat 1925 No1 Vol2 WholeIssue

1/16

~ b e masmanian j}aturalistTHE JOURNAL OF THE

Tasmanian Field Naturalists' ClubNew Series-Vo!. 1. /\ PRIL. 1925 No. 11.

Outlines of Tasmanian GeologySection 11- (Continued)

EROSION BY RUNNING WATER(Continned).

DESTRUCTIVE WORI< OF MAN.Bush Fires.

Man comes along, and. in W!lat he mistakes as his interests alters the wholeface of the country and does so without; t moment's thought to the geology or tothe ultimate results of his actions. Thegreatest mischief-maker is the uncontrolled bush fire. Portions of the countryrequired for agriculture are carefullywatched, but bush fires spread over wideareas of unoccupied land, and one firemay turn a fertile hillside supporting aluxuriant forest growth into a bare, stollYwaste. The fires destroy the vegetation,and the next shower wears out gutters,often down to solid rock, their size devending chiefly on the !dope. Before the, 'egetation can get a start again the surface has been scoured into gl'eat channels, which ,vill gt 'OW from year to year,and the land ruined for many lifetimes.This is occuring everywhere ronnd Hobart. 'Ve should be particula.rb' careful to keep as much vegetation as! possible on onr steep hillsides, until theyare ready for the clm;;e attention of agricu1ture. Instead. fire after fire has ravished them, until in many places, notably on the S!lopes of l\iollnt 'Vellingtoll,all the soil has gone, and the hillsidebare of all but the most firmly established trees. The process may go further. and remove the whole of the soil.leaving only barren rock in the place ofa flourishing jungle. On La Perow;;;e.a bush fire, wantonly Hghted in a beautiful beech forest, even consumed thepeaty Boil. until now the surface of themountain is a veritable desert. Tt wasthe same destructive agent that madeQueenstown and the Linda Valley resem-

(1)

l)le a Somme battlefield. There the trees\vere cut down for firewood, and the llntlergl'owth burnt by a cuccessioll of bushfire:il deliberatel), lighted. Very shortly the excessive rainfall had removedl!very vestige of soil from the steep hillsides and given what thirty years ago\Vas a valley of ferns and 1110::;se8 an aspect of utter desolation.

Clearings.Clearing of land should be undertakenwith great circumspection, as most farmers in hilly country know. As soon

as the natural coating of vegetation isremoved, rain water tends to wear deepchannels, which will, if not prevented,SOon ruin a fertile selection. Throughout Tasmania, which, with its steep slopesand heavy rainfall is particularly liableto this form of "pest," you can see farmFlthat have been ruined through the develovment of these channelt':o The remedy's Nature's drainage and planting.Road Cuttings.

:Mllch damage is often Cansed by thecareless construction of roads runningacross a steep slope. Often a grasFlyhillside can jUt:rt drain off the surplusrainfall without disturbing the snrface.A careless engineer, with two little keenness to think of details, makes. a roarlacross the bottom of the hillside. Sucha, road naturally has a high cllttting onit s upper side.

Over this the water that has beendraining quietly off the gl'assy sloperuns with a velocity increased f. hundredfold. In no time channel-s are cut in theroad bank, and theRe .extend rapidly Hpthe hillside. soon ruining i t for ever. Asimple drain to catch the water on tl.etop of the cutting, and AO prevent itfrom developing momentum by faHil1g'over the steep slope, 'would have prevented this. There are numerous examples


2/16

THE TASMANIAN NATURALISTof paddocks thus ruined round Hobart,notably one just below the lower reservoir.

Another frequent form of stream erosion which has very damaging results isthat originating from the cart track inhill country. A rough track or unmadel'oad is run across a s1ope. The surface is worn down sufficiently to intercept the natural drainage of the hillsideand the check imposed by vegetation isremoved. This track then collects manystreams of water, an..d very soon becomesa miniature gorge, increasing in sizeevery winter. :Many of the streamcourses on the lower slopes of Mount\Vellington were once cart tracks, andmany of the prospectors' tracks throughthe West Coast are now mere groovesworn six feet deep or more in solid rock."Bad Lands."

When an otherwise level or e v e n l y ~sloping piece of country b ~ c o m e s thusscoured and seamed with a bewilderingmaze of deep gutters and s h a r p ~ d i v i d ~ing ridges, It is termed "bad lands."Such are frequent when there has beena sudden alteration of drainage in thenear past. They may extend over apaddock or cover thousands of acres.They are merely an exaggerated exampleof erosions by the small tributaries at thehead of a drainage system, and illustratewhat is going on over the whole land vscape continually, j f imperceptibly.EROSION BY RIVERS.

In the previous sections dealing withthe wearing away of the landsca.pe byrunning water, it was shown how t h ~bulk of the actu q 1 work of erosion wa's doneon the sides and at the heads of thevalleys by the small rills of storm waterthat come into exist-erlce after everyshower. But below these run the streamsand often great rivers which an havetheir bearing on the erosion of the land vscape. Although they can only work intlheir channels and aife'ct a very narrowarea compared with the streamlets already described, they really govern thework of these smaller agents. In thefirst place tbey provide a local base levelfor the rain wa tr channels. The river,although its work is restricted in area,is fa r more powerful than any tributaryin its basin and can wear the bottom ofits valley deeper and more rapidly thanthe water in any of the smaller streams.Thus the bottom of the main v,alley inany region is continually kept the lowestportion of that region. To this level thestreamlets can be alwqys reducing thesurrounding country and they al'e continually at work widening this deeP"St valley. Were it no t for vhis work of the

(2)

river in providing an ever lower base levelthe small streamlets would very soon re duce the valley side to a level beyondwhich water would be unable to flow.In the second place the river removesand distributes the material worn fromthe land surface by the smaller streams.Were this work not done the streamletswould soon cease to flow OD account ofthe accumulation of sediments in thecourse.MECHANISM OF RIVER EROSION.Trhe principles of river erosion are similar for a vast volume of water like theDerwent or the Gordon, and for the8m!Olllest mountain stream and even forthe storm water runnel formed after aheavy showe'r, and these remarks holdgood for them all.In the first place, while a small stream vlet n:ay be aLle to cut it s course ,;alelyin sLft eoil and wear out a course bymerely moving particles of this soil downtIle hill, a ;>p-rmanent stream or ::-iverve!'y soon ~ u t s d o w n ~ in plac es if notthroughout its whole course tt. solid rock,When i t flows over hard rock, mereweight of water, or even volume, or speedof flow can accomplish nothing, and ariver cannot erode it s bed by the s-im)iemethod of pu.hing or tloating porti0Dsof -;-,1 e landscane down its course in fine

~ r a ] ns. The river can only deepe,} its\,,;11 iey by ruhb,ing boulders, p e b b l e ~ . cndS; ' l ld over li'xposed bede of rock tu ;t s

c n ~ T e ( ' As W ~ saw in the case ot !.hesh'ams, the work a river can a co l1p1ishdeppnds on (1) '"he volume of w a t e ~ andtre regularity of the flow, (2) the sl.)pe,(3) tbe hardness of the rock .ver \Vbi. hi t flows and (4) the amount of sedimentit c ~ r r i e s over it s b.dFLOOD TIME.

1t is during flood time that the l'i\"erdr;c.s most of t h ~ work of erOSlOTI. Thenaq tributar::s arli' dischargIng ~ r . ~ ! ' I , t\'o:umes of sedb,eJJt into it, aud the viiit '"nal volume of water CS)!} tran'3pot't:.:trger bouldefl!l. 'DhHile poundi!:tg on andsel'aping over '-,.e :-ork of its bed abvayslpRve "heir md .. ;r in deepened chau ;(.'1


3/16

THE TASMANIAN NATURALISTa floqd may iD scour out the river channel that the ~ l o p e is insufficient to permitthe streams during the succeeding periodof Iow water to transport any sediment.'Vhen a river has reached this stage it canonly erode it s valley when its volumehas been abnormally increased by floods.

THE SLOPE OF THE VALLEY.A ~ explained before an increase in the,;lope of twice gives water a carryingcapacity nine times as great. Therefore,

i t is where the slope is greatest - W1herethe river is running the quickest - thatit is eroding the most. Should a river,after flowing along a very gently slopingvalley. come to a place where, from al'P(,pnt fault or other cause, the slope ishtceper, it will cut back from this place,", deep gorge. This is tihe simple explanation of the Cataract Gorge at Laun-ceston, for example. Here the South Eskflowing for many miles over a very levelplain came to a sudden sharp drop toth 'ramar va1ley, The increased velocityenabled it to cut a considerable gorgein "ery solid diabase here, when furtherinlanJ it haR hardly cut at an into loosepebble drifts. 'Dhe same explanation ncCOUl l ts tor most of our great gorges,

This feature is very noticeable at thl;":ertge of the Central Plateau, and to ales s(:'} extent on al l our flat topped mouutains. Streams which have hardly wornOUT a defined channel for themselves onthp top of the plateaux and at the footwander in wide, shallow, twisting rivers,fiGW in tremendous gorges, over fallsand rapids as they change in level fromth e mountain top to the plains below.'T'he riYer c u t ~ down it s bed largel,rhJ working th e rapids backwards upstream.

THE HARONESS OF THE ROCK.Naturally a valley takes longer toevacuate in hard rock than it does insc fter rock. Thus two streams runnint(pnrallel :-,ud with equal volume and slopeway in time erode very different typesd valleys in different kind of rock. Butin Tasmania variations L! rock beds arc

sc frequent that no considerable streamflews for it s whole course over rock ofone kind. The result of this is that theriver's bed C'onsists of alternating beds ofdiffering hardness. The river naturallywears out a wide, well graded valley il lth(> softer bed, but finds considerable dil.ficulty in cutting through the harder rock.I t will wear out its valley in soft rocken the downstream side of a hard bedwhile this hard bar is scarcely affected.Th. drop from the hard rock to the softer

(3)

bed will be ma.rked and rapids will result. This lP the chief cause of tb e man,\'rupids in our big rivers. Take th e Del",'rent, for example. From above NewNcrfolk downwards i t has evacuated itsbeci in relatively soft mudstone an d her!;'fI(;ws in deep reaches. At Falls it hashad to cross a bar of glasRY trachyte (alaya), Bud has been unable to make muchimpression on it. The change of level ismarked and the river runs in a series ofrapids. The additional power given by thewcrease of rate of flow does not cornpensate for the greater hardness of ther o ~ k at this point. The South Rsk, Merscy, and indeed all our larger rivers sho,,,"the same process at work. \Vhere rapidsoccur usually it will be found that the riveris flowing over a bar of rock harder thanthe average met with on its course.

Above such a hard bar, arr area of softerrcek may be found. The river cannot cutinto this to a depth greater than it is cuttmg into the hard bar below, or it wou\tlcease to flow and have cutting power, sothe erosion of this portion of its valley dep E ' r ~ d s on the rate of erosion Of the hardrock below. Often you can find exam ph.,;where a river has had its rate of ermu()nin a soft rock delayed for a very longpHiod by such a hard bar lower in itll.c(urse, but m time it has cut right throughtiJC hard rock, as for example when thishard rock consists of a relatively thinsheet of lava overlying softer rock.

As .soon as the hard bar disappearstl!c. r l v ~ r starts to cut with great raVldlty mto the softer rock higher un.FJ'('viously it had worn a broad valley inthis area. Now it starts to cut anal ' row valley in the bottom of the olderbrcad one and gives us an example ofwhat is known as a valley within a valJey-a feature common in all basalt coun.try, especially along the North Coast ofTasmania. On the NorthEast Coast, tinand gold deposits, which were once depc'sited in the bed of a river , ~ a l l e y , art'now found a hundred or more feet abovethe river which, having cut through ahard layer, has deepened its valley veryfsst. When a river appears to cut out anarrow valley at an abnormally fast rateafter a long period of gentle erosion thisis often th e cause. '

Another aspect of its rock bed thatimparts distinctive features to a river'scourse is the way in which this rock isb e d d ~ d . ! f it is a. massive, igneous rockbeddmg IS nonexlstant, but if it is astra tified rock its tendency will be towear away along the bedding planes.


4/16

THE TASMANIAN NATURALIST---------------------- -- -- --------The rue!,: will tend to break in slabs andLht' water to work uown joints and cutthE' strata mto blocks goven,lecl by thesejoints. A river's course is often contl'(,dled at infancy by these joints andlater it c,tnIlut move from the course snfermed. Again, if the strata are clippll1g down stream at ('xactiy the slope ofth", valley the water will flow o\'el' it\vithout hin(lnuH'E'. I f it is dipping at ( f harder rock overhanging, thus I!;ivingli S a waterfalL l\lany of our falls on~ a : 1 a l l mountain streams are so formed,

e ~ p e c i a l l y in sandstone ~ o u n t r y , where,ve find mm'lt ,)f these picturesque s c e n i ~oeantieR.

Again, while th e ri,7er is ('utting downthE centre of its valley i t is the smallerstl'eamlets. as we ha,-e explained, thatarc- widening the valley. These can cutmere easily in soft rock than in hard. HOin conntry where the rock is Roft wef t ml to get broad, open, rolling valleYR.\",Lile in country where the rock is hardertlit:' valleys become narrow. steep-i'!idf'(lhorges-the small strt:'amletR heing unahl('le do much towards w"idening: them.

THE SEDIMENT LOAD.This has an impol'tant bearing on theamonnt of work a river can do. Th('riv(>1' (lerivs tlIP sediment it pus:he!'l overbed mainly flom its small tributaries.The amount it ('an carry uepends on thevolume of " .-ater and the rate of flow, hutwhether or Hot the river is supplied withthe maximum amonnt it can carry elependl'l on th e nature of th e r O l l n t r y ~ overwhich the tributary streams ftO\"\', oftennn the recentness and Y01m11e of the rainfall and Oil the absence 01 ' otherwise ofobstructions to th e carriage of sediment.I f the stream Jet tributaries ar e cutting

:t way loose soil or soft rock, or if theabsence of vegetation makes their workens;v. the river ,vill have a considerable(4)

load of sediment, and otherwise if thetributaries are cutting iuto ha rd ' rock.Also if the landscape i::l hilly al l tlwI'otl'earns \\'il1 be assisted by the slope----while the process will be reduced in proportion as the live ing proceeds. I t('ommon knowledge that after recentrains the riw'rs are charged heavily with,'ediments, and it js then that their greatest work is done.

As nn increase of pace gives an increaseof carrying power, the H'YerSC is alsotrue. Anything that teuds to retardth e How of a l'iYer tends to reduce itseroding Dowel'. Thus, if its meets a lakeload il'l deposited in the still w a t e r ~ ,and the outlet is free from sediments.Tlw same applif's in a lesl'ler degree todeep, quiet reaches so often worn by afiYer at intervals in its course. Here theriver is scarcely cutting at al l unless intimes of aunormal iloods the current isstrong enough to scour along these deeppools.

The Shape of the Valley.As the river can only cut iu the bottomof it s valley, and as it alw.1Ys largerand more powerful than any of its tributaries, the valley tends to assume a Yshape, with the bottom of the V in thecentre of the river bed. I f the river i::;

cutting rapidly, and the tributaries slowly,the sid-eR will be steep, 01 ' even precipitous ,,,,hen the river has cut down toa point beyond which it can cut, hut thelittle tributaries will gradually widen thevalley.A stream in newly elevated countrymay commence to flow in 11 perfect];'Rtraight course, but snon it ~ t r l . r t s tohend. slight obstruction, a differencein hardness of the rock, et difference inI';]ope, will al l tend to make the streamdt'Yiat('_ On a bend th e current m o v e ~

faster on the outFdde (a s on the c i r ~cumference of a wheel). and thus b e n d ~tend, by cutting into the outer bank, toenlarge themselves, until any stream wesee today moves in a series of curves. TheRame proceRR gives ll S high banks and often cliffs on the onter Ride each curve,and low banks-sometimes swamps-onthe inner side. Tributaries also flow intothe main stream. The faster the river('nts down its bed th e more power thesptributaries have to cut valleys of theirown. The t\VO processes result in a serif'S of spurs. \\"hich rUll out into th e mainvalley. first from one side nnd then fromthe other. generally ending- at the outerside of a bend_A river valley, therefore. usually prAsents a V-shaped section with numerou5I:s.purs projecting into the valley. You can


5/16

THE TASMANIAN NATURALISTseldom see far along the valley i i standing lleal' the level of the river, and theview is from anywhere restricted by aH...djacent :5pur.If, from any cause the river derivesadditional cutting power, it only accen

tuates these features, as i t cannot moveout of the valley already cut, and merely cuts the sncees.sion of beds deeper.

Section 12-EROSION BY ICEIn high latitumpcrate regions,Huch as Tasmania, the tops of the mOUlltains will first be aifectpd as a glacIalcycle approaches. On all mountains thereare small hollows and pockets in which

(5)

SllGW lies longer than elsewhere. At tilUt'!olbanks of suow will persist throughout amIld summer. These are very frequent on~ l ! our mountains, and snow can always bpfot;ud in the same spots .l.t least up toChristmas time. The8e summer snowLanks on account of their persistence, gradually "dig themselves in." As has beenexplained, frost is a most powerful d6ent01' erosion. Round these snow patchel!lJj naturally colder than on the rest ofthe mountain side, und here frost is ,LtwC'rk longer than eL:;f'v; here. Also the meltmg snow supplies l ( ' J'ltinl1al flow . ofwater W111.'h, soakh;:; l I l t \ ) s.urroundlr.glock, is ready to \ . : x p n n ~ l a! a tear t l H ~particles ~ . ' ThHCRlf' usually filled with chiTlS of l'ork orsnil, the products of thi-s frllRt (li . ;integm wtion. Gradually these sno,,,, lwnks will\,,"ork out fo r themselves an appreciable hollow which, if the glacial cycle is advancing, wiU become the seat of th e ~ l a c i c n .

The Neve.As snow accumulates in greater quantit es than it can be melted . t forms fir8ta permanent snow field. The weight ofa great depth of snow ; 1d the free7.ingadion of the very low temperature soonttirn any considerable accnmulation intoie'. This ice cap covers the highest portions of the landscape, and in time, withthf' increasing pressure of succeeding accu

IlIulations, it starts to move. The directiOn depends on the slope, but in C a S f ~ , 3\If absolutely flat country pressure alonemay force the ice field to creep graduallyout from the centre of greatest accumulations. I f the slope is regular or noneXIstent, the ice will PlC;:. outwards untilit reaches a line where the t e m p e r a t u ] ' ~i high enough to melt each year as muchicf' as the pressure behind forces intoth e locality. I f the slope is not regularthe ice will tend to accumulate in val-1f'Ys, where i t wi11 move as a frozen riverknown as a g1acier. The neve is theaccumulated snow bank or icefield thatfeNh; the glncier, or moving ice sheet..'\, glacier oc('upieF; a vttlkv and. therefor+>IJ ('n" i:-; lIsually exposed above it c r a g ~0: iee-free rocks. The neve, or an 1.('1'>sheet, on the other hand covers


6/16

THE TASMANIAN NATURALISTthe highest portions of a given l a n d ~ ( ' . a p e-only occasional pinnacles J}rojel:: ~ i n g .

Clrques.T1hese snow banks gradually deepentheir seat, and as they do so the forceof niv'ation grows s t r o n g e r ~ and also

has greater surface on whioh to work.The base of the snow line is the pointa t which frost does most of its work.Higher UP. under a permanent snowcap, the rocks are prote,cted from aUernating temperatures, and from e r o ~ i o nby water or wind. Lower down thecold is less intense, but in the Z U l l i : ~. where the sun is continually meltingsnow a t night, and setting free waterto saturate every crevice in the rockface, and the frost a t night is expanding this again as ice, tear ing the rocksapart fragment by fragment, and enlargmg tlie network of t iny cracks fo rthe w'ater from the next thaw to percolate through, we have the maxImumwear and tear.

Although this may occur right rounda symmetrical peak, such features O'Ccur seldom, and the most usual pOSition for the zone of maximum nivationis at the head of the valleys, jus t,,,"here the glaciers emerge from the icesheet. The glacier appears in thisway to gouge a route for its,elf into theg ( ~ n e r a 1 slope of the mountain, andthese huge semi-circles of cliffs (might.:,'3rmchairR on the mounba.in side) aretermed cirques. They presept the mo'>tstriking features of our Tasmanianmountain country, and provide us withour finest scenery. )1any large volumt:b would be required to describe thecil'ques of TaSTIlania, but they arewell known to all who love the mountains. At the head of broad valleysa horsf'shoe of cliffs rise sometimes insteps, sometimes in unbroken walls fora thou sand ('Ir more feet to the narr-owridge of th e mountain crest. The flooris ~ l l w a y s f lat, and Ulsua,]:]y Clcyveredwith the delightful King Billy pine andpretty grass trees, while in most repose the jewels of the highlands, theazurite blue rock t:lrn.

The Lake Judd cirque, on MountAnne, is a gulf cut into the hear t ofthe moullta.in three miles deep. andbounded its whole length by a Circleof cliffs t.hree thousand feet sheer fromthe top of the mountain to the blue waters of th e lake. The so-caned Crate!'Lake, on Cradle );tountain, lies in acirque of white cliffs six hundred feetperppndicular from th e lake's Burfac('.The Lake Belcher eirque, in NationalParI.::, has been shown by several well-

(6)

known photographs, and can er;ual f'4-mnus E:pots in the !Rocky Mountains forpIctureSque and grand mountain scenery.Glaolers.

From their source in the cirques, andfed by the accumulations of the NeveIce, the glaciers are pushed down thevalleys until t.hey reach a point wheretht'} vrcssure from behind is insufficient to replenish the wastage from ineltl IIg. These rivers of ict" have a c'onsic1erablf' bearing on the erosion of thelandscape. In the first place, i,n thecirql1es the water, freed by the mid-day ~ h a w , freezes again a t night, theice of the glacier becomes cemented onto the surfac:e of the cirque wall. The

g I a ~ i e l ' Is continually, if v.ery gradually . moving down the valley, and it ex erts a tremendous pull on the blocksof rock already loosened, as described,by frost, and tears them bodily out oftheir beds. I t is quite common to findblocks so wrenched from cirque wallsscattered through our upland valleys,and Dften they measure f i f ty cubic feet,

. In the second place, th e very weightof ie" does considera.ble work in erodi'hgthe valley over which i t travels. InthiA work i t is assisted by blocks ofrock that find their way to its unders u r f a ~ e , and to blocks which i t picksup as it moves. These, with the enormous weight and power of the moving'ice, tear and scratch away the rocksvf t h t ~ valley floor. A glacier ca n alsoscoop hollows in its bed below thegeneral leveJ, which is impossi,bl. WIthwater. But too much stress must notUt:' plE'ced on the erosive power of glaciers, 'beca.use ~ h e y very easily ride

o v ~ r an obstacle.U Valleys.

As has been explained, a stream ofwater erodes only the very bottom ofits valley. A glacier, however, usually ccverg a much wider bottom than astream does. Also the streams valleyis largely widened by t iny tr ibutaryrIlls. A glacier has nothing to oomparf' with these, and any tr ibutaryg l a c i e r ~ are themselves quite main features. For this reason the sides of aglacial vaI1ey do not tend to widen.Again, a glacier can cut with its sides,WhiCh a river cannot, and the processof nivation which is responsible for the

c i r q u ( ' ~ is at work to some extent alongtlw ~ i ( J e , q of the glacie,r. Here Is maxlmnm fro-st acticn. and the moving icE'C3.11 tOHl' blocke of the rock wall ruway.So (l s a result a glacial valley presentsthe general a.speoct of stra:]ght, often


7/16

THE TASMANIAN NATURALISTprecipitous lSoidE:ls, w l ~ h a broad, flatbottom. They rese'mble in section aU, just as a water-wQ.fJl valley resembles a V. Further, the glacier seldombends, auu tends to shear off protrudin g spurs, giving a glaciaj vaUey amore open aspect, and allowing a lunge rvie,v than is usual with water-wornvalleys.

Such valleys arc very commonthroughout our west coast. The well-In.own view looking from the Lyellmine down the Linda Valley showsthese features to perfection. IIn manyplaces on the weRt coast, for example.3.1ong the head of the Pieman andgreat . tdbutari( 's, the Husskinson,::.Hurchison, and Mclntosh, and furthersouth, from Lake St. Clair, to theVale of Rasseb.s and right down theUpper Huon, the valleys present thLSdistinctive feature.Glaciated L a n d s c a p ~ .

Water i n c n ~ a s e 8 m capacity for er()-sion as it descends a hill. so the general ~ l s p e c t of watet'-worn topographyi& convex, that is, the s ~ o p e incl'easestowards t , h ~ bottom of the hill until t h ' ~ ~zone of deposition is reached, when Itattains the level with a gentle, sweeping curve. Ice-eroded country, on theother hand, owing to the pe,culiar metho d ~ of erosion by nivatlon and pluckmg, becomes rather conclave in genEralslope. The sides of a mountain areo.iren hollowed o:ut in perpendicularcliffs, which may occur anywhere.'l.'hesf' cliffs do not shade off in a curving slave to the valley floor, but ,IlI!lYmeet i t nearly a t a r ight angle. L.;o-lated mountains assume a pointedshape, and valleys are bounded by ragged cliffs. Lakes and waterfall.:;abound. T h e ~ e are a sure indkationof an interruption of the orderly process of erosion. In general ice actiongives the landsca;pe beloved of thephotographer and tOUrIst, the wild,forbidding ranges of the w'st coast' a tonce inspiring as ~ c e n e r y , and heartbreaking- a.s source of livelihood.

Section 14-THE SEA COASTThe seashore, so well kllown tt l 118 all,stands by itself a.s a peculiar, if common,

{eatun' in the landscape with chal'aeteristics all of its own. The border line be-tween land and sea assnmes: variedforms-high cliffs, sandy h e a c h ' ~ , low,barren. roeky shores, range after rangeof sand dunes, swampy reaches ann mUllfiats, all common and often n l t e r n a t i n ~within a short distance. Here we see(7)

intense erosion of a distinct type, andwe often find deposited sediments, theforerunners of new fields.

The general trend of the seashore isusualJy regulated by major fault lines,which bound the elevated blocks of thegloue which rise as land masses. Theserault lines, when originally fixed by earthmovements, may extend in roughly astraight line for many miles, giving astraight coast line, or may consist ofseries of cross faults, giving a serratededge to the land (caUed a serrated coast),or again .may occur in a mosaic pattern,which give.s a repeated series of roughlyredangular salients and indenta t ions(termed a "lobate" coast). The ordinaryerosion agencies soon modify the coast asoutlined by these faults. The end ofriver valleys tend to become bays andeidgcs to pit out as capes. Gradual sinking may produce swamps, and rising ahigh coast line. Alteration of the levelof the sea also has its effects. Eu t still,by looking over a long length of coastthe original trend of the main causingfudol's can be discerned.Waves and Breakers.

vVaves are caused by factors (chieflyail' currents) that disturb the ocean's surface. Friction reduces their effect, anda wave does not move the water belowa certain depth-which depends on its size.[ t is only when the water is so shallowthat the wave effect reaches to the bot-tom that the particular wave becomes anagent of erosion. This, of course, mustoccur sooner or l a t e r ~ as the wave nearsthe shore. When the friction of theshore is great enough to retard the bot-Lom of the wave, the top turns over,often with great force, as a breaker.I f the coast is gently sloping and sandyor muddy, the effect of this is merely to

{lisplace some of the sand ur mud. Themore abruptly the coast rises, the strongerthe force of the wave_ This force is tremendous. At the Blowhole at } J a g l e ~hawk Neck iron stanchions, concretedinto solid rock were completely smashedout of their fastenings, and thick ironrailings, all many feet above high-watermark, were twisted like pieees of fenc-ing wire by one storm. This mere forcehas eonsiderable e f f e c ~ but just as wesaw was the case witn streams, wateralone has really little effect. These wave.are charged with sand, pebbles, and evenlarge boulders, which are hurled againsta high coast or cliff, and break down andtear apart the rocks. The stronger theforce of the waves the bigger the boulders it can hurl at the cliffs, and it is truly!'emarkable the size of the rocks that aresometimes left by a storm high up on a


8/16

THE TASMANIAN NATURALISTclitf ledge. Half a ton boulders hurled;-sO feet above higlH,-ater mark are common n ( ~ C l l r r e n c : e A . Remembering thatthe solidest rocks have joints and linesof weakness, it can easily be understoodIL l t I l l ) cLH IUl 'e l 'an withstand the buffet-ing of storlllY seas for ever.

Cliff Erosion.Chffs al'P,


9/16

THE TASMANIAN NATURALISTthen get caught by the wind and gra-duaJIy moved further from high water mark.In time, sufficient accumulates to form asandy beach; and if the wind is strong,sand dunes begin to grow. High cliffsare usually separated by fine beaches. Onsuch a cuast el'OEIion is active. I f currenk; run strongly and indentationsH bound, the best beaches will be found.I i the prevailing winds are inshore youwill find high sand dunet'!o l'hu5 thestormy \ V e ~ t Coast preBents Ub Tasmania'sfinest beaches, and the rugged South-Easthas many good ones; while the relativelyquiet waters of Bass Strait an-d D'Entre

C i l ~ t r e a n x Channel leave us with low rockcoasts and few stretches of sand.The numerous "tied-islands," or pairs ofi.slallus connected by a narrow sand spitthat abound round out coast, e.g., MariaIsland. Brm.y, South Arm, Tasman'sPeninsula, probably have their origin

likewise, in the droJ)ping of sedimente bythe tide and currents as they are checkedwhen passing th e two islands.Wind piles up th e sand into dunes toa certain height; but unless protected thesame wind tends to blow the top sandlayers off these dunes when they havereached a certain height. Thus th e dunescontinually tend to move inland, oftenspreading destruction over many miles ofcountry, The danger to th e railway linenear Strahan &rom overwhelming dunes isa case in point. The only thing to chet:kthe onward march of th e sand dunes isvegetation. 'Many pleasant fields havebeen ruined by remo\,.-.-ing vegetation nearthe seashore. Cutting trees or burninggrass on a sand dune is as much d crime,and likely to be fraught with as dangerousresults of the lighting of wanton bushf i r e ~ described earlier. A. N. Lewis.

Some Tasmanian FernsIt does not require a person to be abotanist in order to be interested ID theform of a fern. Though they bea r nobeautiful flowers nor offer any ag)'t-eable fruits, thel'13 is somc,thing in th:

gracefulness of foliage which appeals tothe sense of even the indifferent passrrby. To the stUdent there is a muchgrentf:r attra,ction; there is recalled tohis mind the time when the ancestorsof the ferns of the present day coveredthe earth with a mighty vegetation. fUiug up the marshy depressions with the: ~ p e n t spore caRes and decaying lunbs tomake the coal seams of the presentgelleration. There were then no flowering plants, no other trees but primitiveforms related to the conifers, then theern:s. Their relatives, the clUb mOB-ses,grew to noble dimensions of a hundredfeet and more stimulated by the warmhumid atmosphere then obtaining.Few scenes in nature can be morebeautiful than a fern gully. \Vith a background of shrubs and trees th e Old ~ l a l ltree ferns spread their long fronds filliug up every spa-ce where the light of thesun may enter, Though the complete

Mosaic of these Frondsmay appear as though they must absorb every particle of light energy fallingabout them, yet beneath this canopy1:\ f' the plant beings of greatest interestto th e naturalist. Delicate filmy ferns ofmany forms, beautiful names and weirdfungi revel in the fern trunks and moists('il of the depths of the gully, We al l

(9)

note tbe beauty, but how few eal'e toknow more; yet a further acquaintaneewith the structure and life of ferns wi IIadll so much pleasure to a walk inbush that the little amount of thinkingl'equired will amply repay us.

Take the Old Man fern, which ap-peal'S by Its robustness as though Itn l 1 ~ 8 t live throughout the world, aidedin this ambitious delSil'e by the number Jfspares it customarily sheds. for in t l 1 1 ~case of :;he average tree fern theseamount to about fifty million per annum, yet it s distribution appears to bevery restricteu. I t occurs in many partstemperate Australia, also ill New Zealand, but nowhere as luxuriqntly as']'asmania.

Yes, th e average tree fern, after it hascome to maturity, drops from it s frondlSH, fewer than fifty millions of spores, anyone of which may, i f circumstances faVOl' it , eventually grow into an Old Manhee fern itself, But how many of thesefifty millions do really succeed't Examinethe average gully with perhaps a hundl'ed specimens, there are a few thous1-:nd young ones looking quite happy; outof these a few may re,ach th e stage of

b E g i ~ n i n g to form a trunk, but veryfe,,,' mdeed appear to 'Succeed in pushingup their heads, afterA Hundred Years of Effort,

t ~ k e up a position of maturity amongstIts fellows. Perhaps on the average not


10/16


11/16

THE TASMANIAN NATURALISTA llluC'h lllore delicate and handsomeplant is Lady Fern. Thi. bears a largeleaf divided into smaller and smaller divisions till it assumes the appearance of lace.The whole plant is covered with fine hairswhich greatly add to the softness of itsappearance. Accompanying this in wetbush is generally found a robust plantwith tall opening irond. I t is pale green,hairless and fleshy. Someone gave it thename of Oak Fern, which could be improved. There is a group of ferns, somemembel's of which we are bound to meet\..ith. known in t'he "Old Country" ast;pleenwortf3, from someFancied Resemblance to the Spleen.

This grouv is marked by the structure ofthe spore bearing bodies. The mass ofspore sacks is known as a sorus, and ifi t is covered by a membrane when young,this membrane is called an indusium. ASpleenwort may be known by the sorj. being much longer tuan broad, situated on

~ ~ ~ e m ~ : : ~ ~ o ~ ! i ~ d u s l i ~ % . a n ~ h ~ ~ : e r a e r ~ ~ b o u ~half a dozen Spleenworts in Tasmania. The)larine Fern and Shelf Fern are familiarexamples.

M a i d e n ~ h a i r and Parsley Ferns everyone~ ~ ~ ~ S f e ~ ~ l t a : a t f i n ~ t C i ~ l : e C ~ { r t l l ~ ~ ~ ~ ~ l e i ;and Carrot famIly of flowering plants, andyery poisonous. I t is known to chemistsConium, or commonly as Hemlock.Some years ago children on th e NorthCoast were poisoned by eating its seed.

H D ~ r a t e s was compelled to take his ownlife by drinking an infusion of Hemlock

Umbrella Fern i . ofA Very AncIent Type,

and has a peculia.r habit. The leaf isdivided in two a.nd next year a new shootarises from th-e fork of these divisions; theyear after a shoot from each division and80 on. When some years have passed, theleaf is very long, _ with many tiers of annualgrowth. The Wire Fern and the Tangle}l"'ern have a similar habit.

There IS a group of ferns which have astyle of spore bearing rather different fromthat adopted by any others, namely, thewelldeveloped leaf does not bear spores,but the fertile leaf is always shrunken andlooks like part dead fronds. These arecalled Tomarias. This name is soeuphonious and easy, it may very well beeleva ted to the standard or a popularname. The Bro()k Fern already referredto is one of them j another is that verycommon dark ~ r e e n plant so often carpetiog our damp g-uIlies that it may well becalled the Carpet Fern.

The only other ~ r o u p I should like torefer to is that of the Filmy Ferns. Thereare about seven forms o-f them, growingmainly on Treeferns, on bark or sometimes on the ground. Many are of S:ngular beauty, others have special interest forthe student. One forms lines only on thebark of K i l l ~ William Pine. I t is del:selyhairy, and 16 capable of reviving afterhaving been completely dried, a capabilitynot at all common.

L. Rodway.

.Notes on the Scottsdale DistrictA holiday a t SC'ottsctalt: gave milnyportllllities for llature study. and the 101-lowing remarks 2.re extracts fro-m nolesmadE' from tir..Je to time during m y Eta;y

III 1 ha! district.A favorite walk was along a gra,S8Y

1


12/16

THE TASMANIAN KATURALIST' - - ~be a f J . a m e ~ h . l e a s t e d robin on the fence,and his uainty l i t t le brown lady flying:oIomewherc near. Very often the littlethornbill will he there. They are amUR-iug to watch, as they fly on tll(> bentstem of the bracken and twist and h:lJ1aiong it. They appeal' ,1 . t i n i ~ " t o I'di(h'from one end to another in their nQrricdsearch fu r insects. -

"\Vhile resting there watching t h ~ ~ \ > 'birds, I could hear jw:;t the very faintestrustle amongst the delH", lea\"e:'l, anll asI moved the sound ceased, so I care'fully moved away with my w3.1kingstick the surface leaves until I finallydisclosed a young, half-grhwn bluetongup.d lizard (generally misnamed a"goanna") . I t lay partly curled up,\Jut remained quite still while IT admii'Pllits pletty r n a r k i n g ~ and y.ellow-brownspots. t carefully laid the leavE'S overit again to ' see i f i t would move; butI t remained perfectly still.

T h i ~ lane opens out into I t big grassymeadow where young cattle graze:flock!:'! of starling!?, chattering, feAd here.and a pair have their nest in a holea way up near the top of a very talldead gum. There is evidently room toturn, as one bird will fly in and disappearfor a !':cond. and then appears a t thee n t r a l l ~ e and surve):; the fields far lH"I(lw from his lofty home.

Another introduced bird of ..vh:chthere are numbers is the pret ty gold'finch. I t will often alight 011 the to;:>af a thitlltle, no doubt receiving the I am"of thistle-finch from the fact.

A cuckoo will I-lettle OIl the fence an 1th e pipit feeds amongst the gl'aRS; butkeeps his distance from me, as I wendmy w ay down to a sheltered bend ofthe little creek, bordered on this sirlewith blackberry and fallen logs, anathe opposite sidE' with bracken ree "s,young bJackw{)od and wattle, a fp"vgum trees and several deall treps. A firehad evidelltly passed through l a ~ t s mmer.

I have spent many happy h0l1rS t h e ~ ejust listening to the b i r d ~ . and keepingvery quif!t and still. Sometimes aBandicoot Will Come

011t from under thp b-racKtlerry and wander along a t the Hide of the log whereI am sitting. He will feed on the grassand come nearer and work his w ay unrJprm y log, and appear again on thp oth"'rside, so close to me th:lt I could putout my hand and touch him.

A young rahbit peeped out of his re t reat and played abol1t in the grass,then hopped upon a log lying parallel(12)

with .mine. He came quietly along untIlhe was level with me. then sa t up andvery daintily performed an elaboratetoilet, taking much care over the washing of each forepaw. He watched mefor a few minutes, his ears moving ashe listened for any strange sound, thenhe scampered off, his little white tailbobbing, and disappeared into the blackberry.

1'h81'e are only three sounds to hear,the rippling creek. the drowsy murmur,J;>cetles, and flies, and the wonderful~ l l l g i n ~ of many wild birds which fillsth0 air 'with sweEt music. A goldfirchflew down 'from its perch on the boughof a bare t ree ' into a t iny patch of grass,and its perfect rBilC'ction showed dearlyin the wate.r, making a charming moving picture as it m o , , ~ u feeuing in thegrass.

T ~ r e are three black and',\.vhite fantails in a blackwood, and they aJ'P const


13/16

THE TASMANIAN NATURALISTHere I have s ~ e n the fiarnebl'eastedrotil . aad mate, his favorite" tree being a small dead wattle, where hemakes a lovely touch of color perched

O! 1 Cl bough. Both the pallid cuckoo.and the fan-! alled cuckoo are here. andI have watched a t:ny thornbill gIve excitt'd chase to the latter attempting tofly above and making very determinedefforts to Deck at the cuckoo's head.

There is one beautiful firetail here,and appears only just about this p: l r tof the creek. I have ~ e e n i t with itshe:1d into a blackberry bush after in s e c t ~ . appearing Uke '.l very vivid redautumn leaf until it turned i:self about


14/16

THE TASMANIAN NATURALISTand all three cuddled up closely together. Overhead a long, dried frondof the fet'n dropped, and little shaftsof sunlight filtered through the foliage above, touching the soft, downyteuthers of the babies and warmingthem. SittIng thus, they blended perfactly into the coloring around them,and only when they heanl the wel('ume sound of H parent returning withfood. and little heads and yellow beaksmoved. could I see what they were.\Vhen returning from a walk on theLietinnu 1';)1\Willows, whose young, delicate tintedleaves glisten in the sunlight afterrllin. and beautiful yellOW, golden yellow, buttercups stand upright abovetheir dark green foliage, and tiny wildviolets grow thickly upon the bank,keeping c1O!'1e to their mother earth. Inthis Quiet glade at the edge of thedear. funning watel'S of the Little Forrester, overhead. in the tall trees wildpigeons (bronzewlng). pa,rrots, andother birds fly undisturbed, arid giveQuite El romantic finish to the charm ofthe bush. I1a M. Harri.

Some Notes on the " Watile " or " Acacia"The word "wattle" iA one which wC'in Australia have peculiarly adopted Cl"our own. I t dates from Anglo-Saxontimes and signifies twigs or saplings orflexible rods plaited or interwoven together. The ,,",ork has come down tomodern days, and when early Rettlerflcame to Australia they found i t COIlyenient to construct the framework ofthe wans of their dwe11inu:s and other

buildin,z:s of twigs and split sanlings: theoperation was called "wattling" and thematerial used "wattle." Near Sydne;vCoye there grew in abundance. o y e r h a n ~ -the water courses, a small tree withsmall thin flexible stems, which waFl frequently nsed for the pnrpose, nnd hr-ncE?

I

(14)

was ealled "wattle" or "black wattle."Subseqnently other phmts which wcnow call acacias were used for the purpose. aud these are recognised i'lS "wattles" in most parts of this continent or'Australia whether th(!ir stems and twigsare used for wattling or not. The term"wattle" is, however, by no means universally applied to plants of the genusnearin, partirnlarly in the far westernnartfl of the State of New South 'Vales.Myal!. Boree, Mulga, Brigalow, Cooba.nead Finish. Gidp:e-e, Hickory, ~ 1 i l i g e e ,PmbreIIa-bush. vVait-a-whiIe, and Yarranall belong to the great wattle family.The origin of th e name acacia is notabsolutely free from doubt, but the most

t


15/16

THE TASMANIAN NATURALISTreasonable derivation indicates that itcomes from the Greek, Akazo. I sharpen,in allusion to the sharp spines of many ofthe AfrIcan and Asiatic species which are,however, not characteristic of most ofthe Australian ones.

Acacias are foundMainly in the -v.-armer Regionsof the earth, particularly Australia andAfrica; they aggregate nearly 500 speciesfor the whole world, of which considerably over 300 afe found in Australia alone.I t will therefore he seen that acacia, oras we call it "wattle" is mainly A u s ~tl'alian. The number of species can onlybe stated approximately, as botanists COlltinue to discover additional ones.

Blossoms or Flowers.The flowers of wattles fall into twogroups, those which have their flowers insmall round heads or fluffy balls, andthose in which the shape of the flowersmay be described as short blunt rods orspikes; if you look at the blossom witha pocket lens or magnifying glass, youwill observe that i t consists of a verylarge number of tiny flowers, forming infact, a colony of very small :fiowerettes,whose structure, though minute, is as perfect as that of any very large flowergrowing in our gardens. The minuteflowers will be found to contain perfectsepals, petals, and a large number ofstamens together with a pastil, the tinysepals and petals differ amongst themselvesin shape, texture, markings, in the p r ~ -sence or absence of hairs, and as thesecharacters often determine the species, itmay be necessary fo r a botanist to examine minutely a plant submitted for hisopinion. The color of the flowers variesfrom pure white to deep yellow, differentspecies showing flowers of varying shadesof cream color or pale yellow. They dono t show to advantage as cut flowers,their exquisite flnffiness departing verysoon after being removed from the plant.'NIost people are aware that the fruitof the wattle is a pod of legume, whichalthongh varying a good deal in share indifferent species, bears a strong familylikeness to the homely pea or bean. ittherefore belongs to the natural orderleguminosoe. In some seasons the conditions for forming pods are unfavorableover very large areas, and we may

Look for Them in Vain,but those of th e ornamental wattles arewen worthy of collection, as .these plantsare best propagated from seed. I t maybe as well to mention here that theouter coat of the wattle seed is very toughand impervious to moisture, so that itdoes not germinate very readily; there-(15)

fore before sowing wattle seed it needsto be soaked in hot, nearly boiling water,or partly baked, an operation often performed by bush fires, the seed will be indry grass land for many years, and assoon as a fire passes Over the grass acrop of young wattles is the result.Most of the wattles have no leaves,but only leaf .talks, whIch are flattened out, and have the appearance .ofleave8; they are called "Phyllodla,"which is a word made up from twoGl'ee,k ones, and means "like a leaf."The feathery foIl ago of t.he black andsilver and Cootamundra wattles, whichare finely divided SD as to be almostfern1ike, consists of true leawes. Manyof these Phyllodia ore almost endlpss ind ivel'sity of appearance. The fea.theryleaf wattles have a curious hab-it offoldtng theIr leaves at night, and goingto sleep.

Wattles vary very much in size whenfull grown. Some tIny species onlygrow up to about six inches in height,and may be crushed by walking overit , but mOflt of them are shrubs ortrees of moderate size, while at leasttwo species reach the height of verylarge trees, bDth of them being foundto measure up to ne,arly fDur feet indiameter, a.nd some 100 and 150 feet inheight. I have seen silver wattles ashigh as the gum trees, and ally thickness up to tw o feet or over; they growvery tall and straight in forests nearrl vers and in gullies.The wattle has been set apart as

Australia's National Emblem.and this is very appropriate, whenyou consider that i t is easentilflly aflower of winter or early spring, andit s cultivation easy. I t br:ghtens upour ~ a r d e n s and rowsides and mountainside and forests at a season whenthere are few other flowers, ann. noflowers more attractive than yellowones. When these facts are realised weAhall see more wattles adorning thehomes of this bright, sunny la"'d thanwe do at present, for they are themselves 9.n emblem of sunshine. So thea.ppropriateness of the flower being Australia's national emblem is fully demonstrated.

We will consider some varieties of thewattle. First we will take the blackwattle (Acacia Decurrens). I t is theone used for bark stripping, the barkbeing used for tanning purposes,

The w{){l-d. after stripping, makes verygood firClwood; tHe tree also makes verygood shelter trees on farms If left togrow.


16/16

THE TASMANIAN NATURALISTThe silver wattle (Acacia Dealbata) . This tree, as 1 have said before, growsto a great height; it is also stripped forbark for tanning purposes, and is usedfor the manufacture of wood-wOool. ] 'O l 'wood-wool i t is necessary to get treesof this wattle that are grown in gullies,

i.e., quick grown timber, and free fromknots. The wood wool is used for packing al l sorts of fruit. I t could be usedfor work where fibre is used. A baleof wood wool will pack about 500 c a s e ~of apples; a ton of wattle wood of 80cubic feet measurement yields betweenfive and six cwt. of wood wool. Thewood, when dry. after being stripped,is good firewood. Wattle is also usedfor making staves fo r casks, and in thewhaling days a great deal of i t wasused; the casks for holding the whaleoil were made from the wattle, cartwheel spokes and a number of otherboth useful ~ n d very beautiful things.

Blackwood (Acacia Melanoxylon).This variety of the wa.ttle is of themost valUe ble of the Australian timbers. I t is a timber of the highestclass, having a. very orna.mental character, as well as great strength; i t is ahard, close-grained wood, and is verymuch valued and used in making furniture, billiard tables, gun stocks, walkin g sticks, railway and other carriages,.

and al l sorts of cabinet work. It isalso used in boat building ( ~ t 2 r n andstem posts, ribs, rudder) , naves 0'wheds, par ts of organs, pianofot'tes(wound boards and actions), and verymany other purposes too numerous toindividualise. I t is a most useful timber for ('oachbulJ,ders in the bent timuerhranch; i t bends we11, and with propertreatment from the felling and sawingof the timber it SUbstitutes perfectly fOl 'the bent timber in. say, an Austrianchair, and would IO(Jk better, and feeljust as light, It valuable for panelliug, and will be seen in many ( ) f f i c e ~ inthe dtle!"l. It very like AmerJe:ltlwalnut.The blackwood known in Au!'traliathe Mudgerabah tree, and is very mUch

Used as a Shelter Tree.I t is about the only tree that p a s t o r a l ~i::-;ts in that country do not ringbark. Itgrows to a most beautiful tree, havinga t runk vllrying in thickness, and a verylarge spread of branches of dense folinge. It is an ideal shelter tree eitherin summer or winter . I t should beplanted ahm in gullies and foce};ts fot"t imber.

(To be continllC'd)J. C. Breaden.

TasNat 1925 No1 Vol2 WholeIssue

Documents

Transcript of TasNat 1925 No1 Vol2 WholeIssue