PRINCIPLES OF STEREOSCOPIC INSTRU1VmNTATfON FOR PPI PHOTOGRAPHY 621

of the stereo model, Equations (64) and (65)(Xp, Yp ) = normalized coord inates of the loca tion of lhe viewi ng-screen, Eq ua­

tions (66) and (67)(X n, Yn) = normalized coord inates of the target ina radar frame, Eq ua lions

(70) and (71)zn =xn+iYn

l1yp = half the y parallax, as defi ned in Eq ua tion (34)I1Yp =normalized value of l1yp, Equation (68)

6 = angle of the target in the (x/{. , y R) coord inate system, measured coun­terclockwise from the positive x axis

p=apparent radar ground range at the scale of the radar photograph,uncorrected for relief displacement

Descriptions and Airphoto Characteristics

of Desert Landforms

CLARENCE K. DAVIS'

andJAMES T. NEAL 2

ABSTRACT: A brief discussion of desert landforms (£ltd their characteristicappearance on aerial photographs is presented. ilunotated air photos are in­clnded of areas currently being studied at the Terrestrial SciC1lces Laboratory,/lir Force Cambridge Research Laboratories. ilir photo iuterpretatiol1 is plLr­ticularly suited for the assessment of desert surface couditions.

I ~TRODUCTION

AERIAL photographic interpretation offers amost effective and efficient means by

which terrain studies of desert regions maybe undertaken. The Ten'estrial SciencesLaboratory of the Air Force Cambridge Re­search Laboratories is currently conductingsuch studies on selected desert areas in theMiddle East and in the southwestern UnitedStates with emphasis placed on geomorphol­ogy, structural geology, engineering geology,soils, hydrology and vegetation. Tn addi tionto increasing our knowledge of the naturaliJrocesses at work in desert regions, the presen tstudy program should materially aid the AirForce in improving its ability to assess ter­rain in all environments.

During these studies problems have arisenon the interpretation of surface character ofcertain desert landforms. It is anticipatedthat current research in remote sensing willprovide the capability to further the inter­pretability of desert surface conditions.

CAPAI3ILlTIES A~D r.IMITATlO~S OF ARID

REGION PHOTO hTERPRETATIO~

Desert lands allow a great amount of in­formation to be gleaned from aerial photog­gt'aphy; more so than any other climatic re­gion. In deserts the barren rock surfacesclearly reveal fractures, bedding and contacts.The general sparsi ty of vegetation permi tsrunoff to erode gullies that may reAect thegrain size of the soil mantle, Vegetation ishighly specialized and can provide a clue tothe presence of sal ts or the depth to the watertable, Seepage zones and spri ngs reveal theirpresence by darker tones from increasedmoisture and resulting denser vegetation.Practically e\'ery variation in topography isevident \\'ith only a minimum of soil orvegetation to conceal it. The remote southerndesert of Israel, the Negev, was mapped re­cen tly wi th aerial photographs. At the end ofthe program it was stated that this mapwould not ha\'e been possible without aerialphotography (Ben tor, Y. K., 1952, p. 157).

1 Contract Representative, Arctic Inst. of North America, \\'ashington, D. C.2 liLt" USAF, Task Scientist, Terrestrial Sciences Lab. Geophysics Research Directorate, Air

Force Cambridge Research Labs., Bedford, Mass.

PHOTOGRAMMETRIC ENGINEERING

1. RIVER FLOODPLAIl'iS OF THROUGH­

FLOWIl'iG STREAMS

Examples of major rivers rising outside aridregions are the Colorado, the Nile and theEuphrates. These receive sufficient moisturefrom rain or melting snow to maintain theircourses to the sea. Bench-like terraces of sandand gravel may border parts of the fairly nar­row floodplain, and the channel itself mayhave stretches with sand bars. Frequentlyterraces become cemen ted and then may dis­playa zone of caliche. Vegetation may takeadvantage of the abundant supply of waterwith thicker growth emphasizing formerchannels. Through-flowing streams provideaccess routes into and out of desert areaswhile deposits along the floodplain providesand and gravel as well as landing areas forlight aircraft and helicopters.

DESERT LANDFORMS

Deserts are distinguished by interiordrainage; rocky, sandy, alkaline and salinesoils; highly specialized vegetation; duststorms; high daytime temperatures andgreat diurnal range; and very little precipita­tion.

The processes of desert erosion includedeflation, corrosion by wind, sheetfloods, andstream floods. Usually a local base-level ratherthan sea-level controls most of the erosionand transport by water in deserts. The rarerivers that flow through deserts rise in areasoutside the desert and are supplied withsufficient water at their sources to maintaintheir flow to the sea.

The following paragraphs describe brieflythe major landforms that occur in deserts.Having identified a landform, certain validassumptions about surface conditions andengineering potential of the landform thencan be made.

2. STRUCTURAL PLAINS

Where the underlying bedrock rests at alow dip, there is formed a rather flat monot­onous landscape, punctuated by shallow drywashes and local depressions. These struc­tural olains or hamadas may be qui te exten­sive. Bedrock forming structural plains pre­sumably would consist either of sandstones,conglomerates or limestone. Shales in aridregions generally will erode too easily to main­tain the required flat surface. These surfacesof low relief are readily apparent on airphotos, but the identification of the type ofbedrock is made more difficult by the levelsurface and disorganized drainage (Figure 2).

622

0.8

0.7

0.6

0.5

§ 0.45~

O.}

0.2

0.1

0.04000 4500 5000 5500 6000 6500

WAVElENGTH IN ANGSTROMS

(1) SALT BED(2) NON-SALINE DRY PLAYA(J) GRANITE PEDIMENT(4) BRUSH AND WINDBLOWN SAND(5) LAG SURFACE OF RED SCORIA ON SAND(6) BASALTIC LAVA

FTG. 1. Spectral diffuse reRections of desert sur­faces. The graph (after Ashburn and Weldon)illustrates the similarity in reflectance betweeu aplaya with a salt surface and a dry playa with aclay surface.

Certain techniques of interpretation mustbe altered in analyzing features of arid re­gions. For instance. in humid regions co­hesive soils usually are associated wi thdarker tones because these soils retain mois­ture longer than gran ular soils. I n arid regionsthe clay surface of a dry playa often hasgreater reflectance than sand surfaces, andclay and salt have almost the same reRectancewhen dry (Ashburn, E. V., and Weldon, R. G.,1956, p. 585). This emphasizes the difficultyin determining whether a surface is salt orclay-an important decision with respect toengineering potential of the surface (Figure1) .

Microrelief could help to identify the com­position of some surfaces. If one could seecracks in the clay surface or pressure ridgesand pinnacles in salt, the similarity in re­flectance would not be as significant. Thesecracks and pinnacles are not visible at scalesof 1 :40,000 to 1: 60,000. Without shadows toprovide some contrast they may be difficultto see at 1: 5,000.

Other events common in deserts such asdust storms and haze may restrict the inter­pretability of some photography; however, ingeneral the capabilities far exceed the limita­tions. An amazing amount of detail can beinterpreted from conventional black andwhite photography. The use of color hassome supplementary advantages in distin­guishing certain problem surfaces, whereinquite different surficial materials may rendersimilar gray tones on black and whitephotographs.

CHARACTERISTICS OF DESERT LANDFORMS 623

Wind removes the fine-grained products ofweathering from the bedrock surfaces leavinga veneer of residual or lag gravels. In theAl Hamad Plain of eastern Jordan andwestern Iraq, the surface is strewn wi th thechert that weathers out of the underlyinglimestone. Vegetation may be restricted tophreatophytes growing along wadi channelsand halophytes and phreatophytes in andaround local depressions, filled with the fllle­grained particles brought down the wadis. Anyprecipitation falling in such an area runs offthe rocks and gravel-strewn slopes into thewadi channels, eventually to disappear intothe sandy bottoms after a short run. Somemositure may reach nearby depressions onlyto evaporate. Logical places to seek water arealong the main wadi channels and aroundlocal depressions although water from thesemay often be brackish.

Bedrock underlying structural plains maybe used for foundations, or if the rock islimestone, it may be quarried for stone, limeor cement. The wadi channels contain sandand gravel. Depressions may be consideredfor landing sites depending on their size.

3. PLAYAS

Playas occur in the lowest portions ofinterior basins and from time to time becomethe beds of ephemeral shallow lakes (Figure3). Numerous playas marking the sites ofPleistocene lakes occur in the arid westernUnited States. Some of these still receivewater and sediments, but the water evapo-

FTG. 2. Structural plain, eastern Jorc1an. Bedrockforming this structural plain consists of limestoneresting at a low dip. Dark-toned lava has noodedpart of the surface providing some relief to anotherwise monotonous landscape. The light­toned area in the foreground is a shallow depres­sion slowly being filled with fine-grained sedi­ments.-USAF

FTG. 3. Interior basin and Aanking ranges,northern Nevada. Smokelike dust can be seenbeing blown off the surface of this soft playa andacross the bordering mountains. Surfaces like thisbecome quite powdery when dry, and strongwinds may stir up appreciable amounts of dust.­USAF

rates rapidly. A series of playas may bestrung together by subterranean drainage sothat water can move through the entire basin,a process which may prevent salt from form­ing except perhaps in the lowest playa of theseries. Playa-like depressions occur in otherdeserts of the world although these may notbe playas in the strict sense of the word.

Playas have many geological differencesand have been distinguished accordingly(Clements, T. et at., 1955, pp. 10, 11). Forpurposes of photo interpretation, playas maybe classi fied more si mply according to therelative firmness or hardness of the surface;thus, hard and soft.

Soft playas generally occur in areas ofgroundwater discharge (Figure 4). This type

624 PHOTOGRAMMETRIC ENGINEERING

of playa incl udes surfaces that are moist andsal t-encrusted as well as surfaces that arerather dry but puffy with thin, intermittentstains of salt. Soft playa surfaces may be dis­tinguished on aerial photos chiefly by lines ofdrainage, but also by an intricate pattern oftones, ranging from light to dark (Figure S).The proximity of the watertable to the sur­face, generally within ten to fifteen feet,allows water to rise by capillary action. \Vaterhaving reached the surface evaporates toform salt pinnacles and pressure ridges.Such as does not quite reach the surfacedeposits salt in the sediments to form abumpy, puffy surface. This consists of a thincrust of clay and silt over several inches ofloose powdery material.

Hard playas, in contrast, have firm dryclay surfaces that can support heavy vehicles.These dry playas are distinguished on airphotos by lack of well-defined drainage Ii nes,by an even light-gray tone when dry, and bylarge desiccation cracks. Islands of vegetationalso may be used to distinguish hard playas,

as may dark-toned stripes that occur nearthe playa edge (See Figure 4). Occasionally aseries of darker tones of gray on a playa be­tray a recent stand of water and express avariation in the degree to which the surfacehas dried and hardened (Figure 6). Dryplayas generally are sources of potable water,but it may be deep and occasionally too salinefor human consumption. Potable water usu­ally may be obtained from sandier sedimentsbordering the playa. Hard playas are fre­quently utilized as auxiliary landing fields.In the western United States some of thesesurfaces are utilized for emergency andscheduled landings by the X-iS aircraft.

Exceptions to this two-fold playa classi fica­tion exist, as several playas possess extremelyhard salt crusts, while retaining the essentialcharacteristics of soft playas. Several hardplayas of dry clay are known which possessrelatively soft surfaces. In addition, someplayas exhibit characteristics of both types.This system has proven valid for hundreds ofplayas.

FIG. 4. Surfaces of some playas. UjJper left, southern ~evada. A mud-cracked, dry clay surface of atypical hard playa is illustra ted. lote there is virtually no wheel impression. Upper right, sou thernCalifornia. The puffy, clay-encrusted surface of a typical soft playa is illustrated. Note the two-inchwheel impression. Lower left, southern Nevada. A hard dry playa is illustrated. The vegetation whichoccurs adjacent to the barren part of the playa bears some resemblance to that which grows on desertflats. Note the island of rock in the upper right portion of this playa. Lower righi, southern California.These peculiar stripes of vegetation, here growing adjacent to the playa, also have been observed inwashes in the arid regions of the Middle East.-USAF

CHARACTERISTICS OF DESERT LANDFORMS 625

FIG. 5. Soft playa, eastern Nevada. The frequency of drainage on the surface and the intricate patterllof tones indicate the surface of this playa is moist. The water moves to the lower part of the playa wherethe surface has become puffy and encrusted with salt. Scale 1:96,OOO.-USGS

Playas occupying the low centers of desertbasins or bolsons are rimmed by a series oflandforms each distinguished by an increasein slope over the landform directly below.These landforms start wi th the desert flatbordering the playa, and rise through theencroaching alluvial fans onto the steeperpediment until the front of the borderingmountains is reached. The slopes vary froma few minutes on the flat to a degree or so onthe lower fans, increasing to seven degrees orso on the pediment. The mountain front usu­ally is quite steep varying from 15 degreesto nearly vertical (Thornbury, \\1. D., 1954,p.284).

The retreat of the mountain front and theformation of these landforms is accomplished

by backweathering, sheetwash or sheetflooderosion, and lateral planation. Thus the baseof the mountains is planed off to carve a pedi­ment, and the debris is fl ushed further downthe slope to help form coarse-grained fansand bajadas. Some sand and gravel are trans­ported further into the basin to be depositedas the desert flat, while the fine-grainedparticles ultimately reach the playa (Figure7) .

4. DESERT FLAT

This landform comprises a tranSitIOn zonebetween playa and alluvial fan, and displayson the aerial photo some of the characteristicsof both. Frequently a distinct change in tonesignals the edge of the playa and the start of

626 PHOTOGRAMMETRIC ENGINEERING

the flat. A sudden increase in vegetation, thepresence of small dunes, and the lack of pro­nounced drainage also distinguish the desertflat from the playa and the alluvial fan(Figure 8). Desert flats are composed of sandand silt with some gravel and occasional de­pressions floored with clay that resemble ex­tensions of the playa. Subsurface lenses ofsand and gravel provide channels and poolsfor the accumulation of water to be tappedby wells. Vehicles may cross desert flats with­out too much difficulty provided areas of softsand are avoided. Occasionally the clay areasare large enough to be utilized as landingstrips.

S. ALLUVIAL FANS AND BAJ ADAS

Alluvial fans are those fan- and cone-shaped

deposits immediately apparent on air photos.Fans are formed where streams emerge fromtheir steeper mountain canyons. As morestreams along a mountain front construct fansand as the fans grow in extent, they eventu­ally merge into an extensive alluvial apron orbajada. The surfaces of these landforms aredistinguished by the numerous distributariesradiating from the mouth of the canyon(Figure 9). Fans and bajadas both are com­posed of cobble and boulder gravels andgravelly sand with some silt. The sedimentsare poorly sorted and poorly graded, and ingeneral the material varies from coarser atthe apex to finer at the base. Alluvial fansfrequently are drilled for water. The depthof the water table varies from area to area,but the densi ty of vegetation someti mes is a

FIG. 6. Hard clay playa, western f':evada. Shallow ephemeral sheets of water that occupy parts of aplaya leave surface stains, causing tonal variations such as seen on this dry lake. At times in the history ofthe ancient.lake some strand lines may have stood offshore as bars, trapping fine sediments behind andforming playas in miniature. These strand lines continue to trap sediments during the infrequent rains inthis area. The miniature playas are distinguished by light tones similar to those of the main playa. Recen tdrainage has breached the strand lines in a number of places. Scale 1:96,OOO.-USGS

CROSS· SECTION THROUGH DESERT LANDFORMS

LANDFORM A;'@~~X PI CHARACTERISTICS

DESERTFLAT

ALLUVIALFAN

DESERT MOUNTAINS MAY

FIG. 7. Cross-section through desert landforms. This cross-section illustrates an idealized desertbasin. Characteristics and problems of interpretation are tabulated.

FIG. 8. Desert flat and playa transition, southern California. The barren, hard clay playa changes tolow dunes stippled by vegetation. Patches of the playa floor appear between some dunes. A strand lineof the ancient lake distinguishes this desert flat. Scale 1 :32,OOO.-PMA

-

628 PHOTOGRAMMETRIC ENGINEERING

c1 ue. The shallower water table at the base ofthe fan may cause springs and seepage zonesto occur.

Fans and bajadas are a source of sand andgravel. Vehicles may experience some diffi­culty in traversing the fans depending on thefrequency and depth of the distributaries. Thelower slopes of these landforms may beutilized as sites for landing strips for airplanesprovided the strips are laid out parallel toinstead of transverse to the drainage. Thisorien tation avoids unnecessary fills and subse­q uen t washou ts from flash floods down thedis tri b utaries.

6. PEDIMENTS

Pediments are the slightly inclined rockplains extending from near the base of the

mountain rim down toward the basin wherethey disappear beneath the bajada or alluvialfan. Pediments may be distinguished on airphotos by residual knobs of bedrock, and bya greater slope than the adjoining alluvialfans (Figure 10). At times the boundary be­tween fan and pediment is vague and indis­tinct, especially when the upper twenty feetconsists of alluvial material. Pediments maybe considered as a transition zone betweenthe alluvial fans and the mountain front.Some information about minimum thicknessof the soil mantle as well as its compositionmay be obtained from air photos by analysisof the gullies and wadi courses. Any soilmantle over pediments is well-drained, andthe sloping rock surface beneath ordinarilydoes not permit water to accumulate. Vegeta-

FTG. 9. Alluvial fans and pediment, central Nevada. Coalesced alluvial fans being deposited in thisnarrow valley are burying the pediment surface. The linearity of the mountain front indicates that thecontact between pedimen t and mountains is a fault scarp. Scale 1 :96,OOO.-USGS

CHARACTERISTICS OF DESERT LANDFOR [S 629

FIG. 10. Pcdimcnt and desert mountains, northern Xevada. Outlicrs or inselbergs of dipping sedi­mentary rock rise above the surface of the pediment, covered with allu\'ial sands and gravel. Thc for III

of these outliers indicates that this pediment has been formcd across thc face of the bedding. Scale1:96,000.-USGS

tion therefore will seek out fractures, hollows,and obstructions to the movemen t of watersuch as dikes. The pediments are sources ofgravel, and the wadis are good sources ofsand.

7. DESERT DOMES

This landform ideally represen ts the ul ti­mate stage in the cycle of desert erosion. Itmay be formed on any kind of rock and OCcurSwhen pediments finally cut through moun­tains to intersect each other, lea\'ing a fewisolated residual knobs of bedrock. This sur­face also has been called a pediplain to dis­tinguish it from the peneplain of the humiderosion cycle. Some xerophytic vegetationmay exist on the higher parts of desert domes.Because desert domes are essentially exten-

si ve pedi men ts, the same restrictions on vege­tation and water that apply to pediments,also apply to the upper surfaces of desertdomes.

8. DESERT MOUi\TAINS

Upland surfaces in the desert vary fromlow isolated hills to relatively prominentranges; hOIl'ever, mountains tall enough tointercept precipitation and support stands oftimber, do not belong in desert climatic re­gions.

These upland surfaces may consist of sedi­mentary, igneous, or metamorphic rocks, orany combination of the three. The mountainsthemselves are recognized by their increasedrelief, while the type of rock may be identi­fied by the shape of the topography, by the

-------------------------

630 PHOTOGRAMMETRIC ENGINEERING

pattern of drainage, and by other more sub­tle cl ues such as beddi ng and fracture pat­terns.

Material weathered from rocks of themountains moves down slope coming first torest perhaps on a pediment. Flash floods carrygreat amounts of alluvial material out on thefans. Sand, sil t and some fine gravel eventuallyreach the depression or low area and settlethere. The type and nature of the rockgreatly affect the amoun t and to some exten tthe coarseness of the alluvial material.

The availability of water depends on thepresence of channels or layers through whichwater can move and areas of confinement in

which water can collect. Springs and seepagezones may be discerned on aerial photographsnot only from the dark tones of increasedmoisture, but also from the increased vegeta­tion taking advantage of the water.

The various kinds of rock found in desertmountains may be used for foundations,crushed rock, lime, or road material.

9. DUNES

Approximately one-third of the area ofarid regions is covered with sand (Holm,D. A., 1960, p. 1369) available for the windto work into dunes, their shape dependingchiefly on the direction and continuity of the

FIG. II. Desert mountains, alluvial fans, and sand dunes, southern California. Nearby mountains ofsedimentary rock are the source of granular material feeding these large fans. A band of variously orienteddunes rings the low center of this basin. Eddying winds have disrupted the striking linear pattern of thesand and have piled up the highest dunes. Scale 1:96,OOO.-USGS

CHARACTERISTICS OF DESERT LANDFORMS 631

wind. Dunes occur as long transverse ridgesor seifs, crescen tic hills or barchans, trans­verse dunes, sigmoidal dunes, and fishhookdunes (Figure 11). Dunes may change theirshape as the wind shifts direction. Driftingsand also may pile in the lee of obstructionsforming sand shado\\'s. At times vegetationmay stabilize dunes and prevent their move­ment. Water may be tapped by drilling atthe base of a dune. Dunes may provideshelter for aircraft~a barchan resembles ahuge revetment. The interdune floor may beswept clean of sand and so afford easy goingfor vehicles.

10. DRAINAGE

In the desert every line of drainage is ap­parent on aerial photography~each gully,each rill, each wadi, as well as springs andseepage zones. The patterns of drainageeverywhere are obvious.

Gullies cut into the surface of the soil­mantle reflect the gross grain size present.The cross-section varies to indicate clay, silt,sand, and gravel. Vegetation frequently growsalong the active "'ater courses. In a wide­bottom wadi with several channels present,vegetation may help differentiate between ac­ti ve and abandoned chan nels. \\'adis aresources of sand and gravel and may betapped for ,,·ater. Bars and terraces may beused by aircraft as emergency landing sites.

SUMMARY

Arid regions are particularly suited for airphoto interpretation. Much accurate informa­tion about surface conditions may be ob­tained by identifying the desert landforms onstandard black-and-white photography atsuch scales as 1: 30,000 to 1: 40,000. A t thesescales, however, some microrelief features ofterrain such as low scarps, salt pinnacles,and large boulders important for engineeringconsiderations cannot be seen. To determineif they are present there are needed eitheradditional photography at larger scales orlenses and fil ms capable of resol vi ng micro­relief at scales of 1 :30,000 or 1 :40,000.

Additional research is necessary not only toimprove methods of acquiring information,but also to improve the ability to interpretthe data. The Air Force Cambridge ResearchLaboratories are conducting inhouse research,and are sponsoring programs that ultimatelyshould benefit studies of desert terrain. Theseresearch programs include:

1. REMOTE SEl"SING OF ENVIRONME)/T

The use of radar, infrared, and otherelectromagnetic sensors is being studied inaddition to air-droppable devices capable ofyielding information on physical properties ofthe terrain. Soil samples are being studiedunder controlled conditions in the laboratorywith infrared and radar sensors to determinewhether a catalog of soil measurements can beobtained and used for eventual comparisonwith actual field data.

2. RESEARCH ON I1\OIVIDUAL TYPES OF TER­

RAIN FEATURES

Several field and laboratory investigationsare in progress which ultimately may aid thephoto interpreter in assessing surface condi­tions. These studies include mineralogy andsoils, hydrology, sedimentation, and engineer­ing properties. Landforms of curren tin terestare desert flats and playas.

3. LA1o:0FORM DISTlliBUTION MAPS

These maps are being prepared for theNorth African deserts. This research will pro­vide further delineation of terrain variationswhich occur in the vast expanse of the Sa­haran, Nubian, and Arabian Deserts. Airphoto analysis is an integral part of this in­vestigation,

REFEREl"CES

1. Bentor, Yaakow K, 1952, "Air-Photographsand Geological Mapping with Special Referenceto the Geological Conditions in the Negev,"Ceolog1'cal Institute (Israel), P1tbl~cattOn 3,Jerusalem, p. 157.

2, Ashburn, Edward V. and Weldon, Rodney G.,1956, "Spectral Diffuse Retlectance of DesertSurfaces," Journal of the Optical Society ofAmerica, Volume 46, Number 8, p. 585.

3. Clements, Thomas; Mann, John F.; Merriam,Richard 1-1.; and Stone, Richard 0.; 1955, "AnEvaluation of Types and Scales of AerialPhotographs for Use in Arid Regions," De­partment of Geology, UniverEity of_ SouthernCalifornia, Air Force Contract No. AF 33(616)­2175, p. 10, 11.See also: Clements, Thomas; Merriam, Rich­ard H.; Stone, Richard 0.; Eymann, James L.;Reade, Harold L.; 1957, "A Study of DesertSurface Conditions," Department of Geology,University of Southern California, TechnicalReport EP-53 for Quartermaster Resear~h ';lndDevelopment Center, . S. Army, NatIck,Massachusetts, p. 5, 6.

4. Thornbury, \\'illiam D., 1954, "Principles ofGeomorphology," John \'\'iley and Sons, Inc.,New York, p. 284.

5. Holm, Donald A., 1960, "Desert Geomorphol­ogy in the Arabian Peninsula, Science, Volume132, j\; umber 3437, p. 1369.