Report No. 38
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COLONY AND PROTECTORATEPROTECTORATIC 0FOF KENYA
GEOLOGICAL SURVEY OF KENYA
}-i GEOLOGY
OF THE J MWIN‘GIMWINGI AREA, NORTH KITUlKITUI
DEGREE SHEET 45, SOUTH-WEST QUARTER (with coloured geological map)
I)byy
The late A. F. CROWTHER, B.Sc.,B.Sc.. F.G.S. Geologist
1957I957
PRIN'I'EDPRINTED BY THE GOVL-ZRNMFNiGOVERNMENT PRINTER,PRiNI'L-‘R, NAIROBI Prk'c:Price: Sh. If}10
IS! FOREWORDl- { ”Hi“ { )R I)
The geological survey of the Mwingi areai] E'L‘ii \'\was\i‘. carried' out by Mr. Crowther as part of the primary mapping of Kenya, with the assistanceL:‘-\|\'l‘ of funds provided under the Colonial ..,‘. I Development and Welfare Act. Before he could\\ LIIL. bring his report to its final stages he was :cmh called up for military training and ...subsequently was retained in the Kenya Regiment. He served with the Regiment in KenyaCilgiz; fromii. :11 the[EN-'- beginning of 1953, but unfortunately lost his life in February, 1954, in ;:a skirmishakii'mixh withuiLEi terrorists.Lei" To prevent undue delay in publication, the first draft of his report hadhmi beenhL‘cu :1completedimr‘icicd and:izui amended on his behalf in 1953, but he had not had the opportunity toin readrun! the- proposed final draft before his death. In preparing the final draft everymu} attemptLlncriip‘a wasuh maden;- where possible to preserve the original outline and the2hr ii'cndtrend ul‘of 1hrthe :iiilhm’sauthor's I.‘Il‘|_!g.i!1\.thoughts.
TheEiic aii'cuarea cmleast v!of Muiiigi.Mwingi, :1a \iilugcvillage m‘.on 1!:cthe run-Jroad I'i'nmfrom \iii';Nairobi through Garissa to the \aii’lilui'l‘.Northern Pi'mii‘iccProvince m”of KcnyaKenya ;li‘.'Ciand ItalianHill I‘ Sm‘Somaliland,flziiiiuiui. i‘c-gzimcbecame ki‘H-c.‘known to people in Kenya wi‘non nccuumaccount 01‘of ua g‘ui‘mpczloi‘prospector's \ mmrcamp r.and. factory' Jan :1:at \3Nguni:.i Microwhere chalks,kflJi-i‘, . whitening powders and mmcrulmineral pigmcmxpigments “cu:were pi'cgmrprepared. IUnfortunatelynl'ui‘iiii ': ' littleitlu rim:else (11'of m.-mineral. value' “L- has been foundliquid in 111::the :ii‘cu.area. i\'3..Mr. (Crowther's['U\\ii]L‘!' \ [1‘reporti givesbiwx (Ia i‘i'j-cibrief 'ic-JJIJIEEaccount 01'of the general‘:=Ci’;i] ut‘uiuuxgeology of Elmthe L»district,I. \pi‘gialspecial ampemphasisNix hcii‘wbeing laid|_iiL. mion "asmallfliili: iiILEL'r-ultra-basic" intrusionsii‘;‘.1’ii\iui‘n iiiin |[\its 431151011eastern l‘dii.part. ‘ - \ . L‘.. L' T.The’ intrusions|I13I'Li')iL‘-i1\ are ul‘of 'ia .kind1L! lit-:11that in numcmmnumerous punsparts Hiof the \xurliiworld uir'i‘contain valuable‘»'.i|'.:'.mIL‘ metallicmun .i: m.or nun—meldilicnon-metallic minerals,mi Julia. Lindand ilmugiithough lhcii'their 11!'(1\]‘¢'J{\prospects muare not1 'riupcii'ihopeful iin view of the results1x “Iof thethe: T‘['€\C‘H[presentJ HIRE}.survey, 'it ix.is nu:not iinpmsihicimpossible 511:1!that mm:more intensivelunxixu prospectingPac- might revealam cal \I‘Crdiismall dept-Hmdeposits ulof \lici‘.such ulnar-ahminerals Ll\as 11:;magnesitemew-it aandmi .i\i"t‘\1l‘-\.asbestos.
Forhii' wmcsome ycmxyears rumoursi'umnui's Innshave persistedpuixislmi l‘-iof thealt-L- ncwi’rcm‘coccurrence u!‘of gnu:coal in thei:. C northerniil‘iiiiC i1 parts|‘-;i!'l~ Miof {hethe kiln]Kitui iiiwz'iui.district. Mr. (.Crowther'm'LhCi' mink"made Ll.a ape-gm!special mam“;investigation[iiit‘l] miof 2.9.:the z'cl‘i“:'{cL‘ireported [iii-JRfinds hall.but, :1\as \‘(3\was Upctlcdexpected J‘I'UIHfrom lhcthe guniog}geology nl'of Ehuthe LiI‘CLLarea, \\Li\was Liiiuhkunable Into findIii‘iLi Lin}any Era-cctrace v:of gnu!coal uror possiblyi‘iwxibi} g:‘;l|—ht;il'ingcoal-bearing iWULiK.beds. ThereiiCl'C L1H]can hebe noI‘:I- Linilhidoubt Ii‘:;':'that L‘i‘u"coal inul'idfound in \UL‘i1such munareas Ixis thec relics[-QEiL‘x of war- timeaim-c dumps. .
WILLIAM\\H Li ‘-.\E PULFREY, Nairobi,\L.i nhi. Chid Geologist. 15th". November,\nxcmhcr 1954.I”. ii‘\i?2\!.‘~CONTENTS PAGE Abstract I-Introduction 1 II-Previous Geological Work 2 III-Physiography 2 IV-Summary of Geology 4 V-Details of Geology.. 5 I. Basement System 5 2. Pleistocene and Recent 10 3. Intrusives 10 VI-Metamorphism 16 VII-Structures 17 VIIT-Economic Geology. . 19 1. Basement System. . 19 (I) Garnet and sillimanite 19 (2) Limestone and marble 19 (3) Pigments and gypsum 19 2. Ultra-basic intrusions 19 (I) Magnesite. : 20 (2) Anthophyllite asbestos 20 3. Superficial Deposits 20 (I) Sand. . 20 (2) Road-metal 20 (3) Building material 20 4. Alleged coal deposits 20 5. Water. . 20 (I) Surface water 20 (2) Ground water. . 20 IX-References 21
ILLUSTRAH ‘N'! nONS
Fig. I.-Physiographic units 3 Fig. 2.-Geological Sketch of Kamuthengi hill I I Fig. "3.-Diagrammatic microscope drawings 12 Fig. 4.-Structures in the Mwingi area. . 18 Plate T.-(a) View south from Gai showing peneplains 7 (b) Leucocratic biotite gneiss enclosing melanocratic masses 7 Plate II.-(a) Leucocratic biotite gneiss enclosing folded melanocratic bands 8 (b) Melanocratic biotite-rich band, bent and injected by quartzo-felspathic material 8 MAP
Geological map of the Mwingi Area, North Kitui (degree sheet 45, south-west quarter) Scale I :125,000 . . .. At end ,...
ABSTRACT\BS'I R \( '!
TheIM- report'cnn: duxudescribesflwx .man x-area in the northernAIM-1'»V partmm ofmi the1“; Kamba‘mmflm Native\‘mwc ReserveRcwl'xc 1in central Kenya. It' is‘ approximatelya‘mwn ; 1,200 squareAg ‘7‘mileso in\ extent“1;“! \vandMi is\ l‘wmxigxbounded by latitudes 0° 30' S. and 1° 00' S. and by meridians 38° 00'w E.; and, M 38°w 30' E.} PhysiographicallyI"wj.\1~~ it can be divided into three units:Al m (I)‘111the Mumoni- mountainsT‘IL‘L‘ L1 w“ in‘7 theI'm‘ north-west,14‘72 \“V-(‘L (2) relatively high ground in the west that is‘V\ copsideredLxW"\Lk"k\' toU‘ be\‘L‘ ad remnant[\ZW'K W Nof thesm- sub-Miocenew,.:¥\'mccnc peneplain,:‘cmpkmx which is also represented by the topsmw ofw' \Mmu'cu‘.scattered monadnocksHM :‘mUJ‘wdm ‘Hin the \LMJIILL‘I'lisouthern half :H'iof the area, and (3) a low-lying peneplainLq‘ v.1"! ofM presumed:V'cwxmui end-TertiaryuuirTum: u agemix"in the9::1"~'1'1':L111u,‘;_;\1north and east.
‘, . ,~ ,‘.‘. The area is made ‘.‘up mainly11.1’ of highly metamorphosed.«L and granitized sedimentary rocks of the Basement System of-East Africa. -It includes calcareous, semi-calcareous,VQHZ pelitic, semi-peliticg .,.r"\,*and psammiticnw'T'V‘MLL‘ types.Mp In the east the‘r: metamorphicIzm‘mmmplm' numbrocks have1mm twcwbeen invadedExxudcd Ia}by small ultra-basic‘,'.fl1iji\t\l£ plugs.“Myra, DetailsHum 4‘:are givenIn": ofw the petrology,[NUTKUWIAV‘VJA‘ petrography,wwwpna u"?and {Q‘VIMVH‘Leconomic minerals of the rocks and of the water-supply of the area.
-~ GEOLOGY OF THE MWINGI\lWlXGi AREA.-\RE.\
I-INTRODUCTIONI --l\'I'R()l)L( H()\
The1‘1; \_'\‘1!i'l‘country" describedL‘VQ‘CL‘L‘L in this report is quarter-degree sheet 45 S.W. (Kenya), bounded "\_\by latitudes“ind-b 1? ° 00' S. and 0° 30' S. and by longitudes 38° 00' E. and 38° 30' E. It has an area ofm- aboutghoul 1,200 square miles and lies in the northern portion of the Kitui district of the Southern Province of Kenya, forming part of the Kamba native reserve. Itl'. isw inhabitedHinfzmm byh) about.L'PML'. 30,000Ftwm Wakamba“ukunitm who_‘ subsistmiww byPg. theMic cultivationg 1L.‘_.m‘1. of maize, beansE‘CLIIMKHQi]1i!:CL._\IILtI").and millet, and by herdinghurdm; cattlec.1L11c.-.miand goats.gym. At\! Nguni\"LHH «~11on the1.1m £1.=1'i~\._w.v-“Garissa road there is a camp(“min founded1‘“q by1.. E.y!"G.' Powellp_w L‘j' but“‘_.'. -subsequently.. 1 ‘_ ' acquired." _.,‘' i by1‘. TulaI‘m: Products1), . Ltd., a sub- sidiary of Diadem Products Ltd., where 'gypsum from the Tula valley, near Garissa, is processed for the manufacture of plaster of paris, chalks and whitening blocks. Powell also collected from the roots of certain thorn trees a vegetable' fibre'Whicll be ..baled and sold under the name "flotite" as an insulator, and originally as a substitute for ktttm\ 111life belts. Mwingi is theit‘c mainimm‘. villagewit and hascm.1Pna postfiur‘office,flgun{tuir'kwwmik'a market and Indian-owned1‘ J. HL‘L“ \f‘vL-l"shops, and. is1‘ theU'c scenewax”- ofm“ cattlewith auctions..L'nmnx. Itf'. lies1 on‘11. the11:: Garissa-Nairobi(.mzwu. \uw'fi road, which runs:_:vn. acrossn'nxx the1" southern~\‘-.il'.‘.:_"V portionDu: um of the area and forms\ the1h“ mainnun lineHTL' ofm' communication0‘W'.IT.'1\..LM" '.Hto the50 railway.. at Thika,l'ililxu. 80\‘U miles{1111l J.away. A railway{mu} wasWm plannedPiummd duringAw" ' the[11: 1939-1945NF“; IV-li ‘mu'war toIn runWC.“through U"Gai toLL‘ theL": Northern\L=I"."1L Province.xcc hmbut the projectrmiicg‘. wasum abandonedV‘mtwdmwcfi when"$1193? NH;only the1%- ~11'xsurveying and grading of‘Hthefic rail-bed[ml-"Jed hashm beenNu!" carriedcm m1 outUNI asm farJ'L-J asm the111C Mwingi-Katze\Iw» ‘ g1 "L" road.Imus. BesidesBows.» the' Nairobi-GarissaCumin” road,zumi'. which\w‘H‘ is\\ maintainedHZLLH'HSHWL‘C byh} the PublicI’ut‘iu: \\\.“}\wWorks Department,qu'fl 117. therethat isix .=a good system" of Local Native-; Council(mu-13‘. roadsHuck thatH141 .tr'a‘are usableLmihlc duringduhng theHm dryin weather,“.czgmct'. but3511’. become difficult during the rains. RainR1: H fallsmm inm theHTC area“[111{:7mummm:xmxm‘x.in two distinct seasons, from(mm March\Im‘ch toIn May,Mn}. and.md. mmduring‘ ' November\mctnhu and«1U December.”camber. The"1 HQ rain,mm. whichux'mu'n falls“Mk mainlynumb in'H the evening,waning. is:\ ofu” theihc.heavyH wuwcglmmwconvectional typemm: andmm] theIn: amountmtm‘vm‘: atM anyn placeNiuuc isix conditionedmm! Mum‘s; byh} itsm proximityi‘wwmxl} to10mg»high ground.a-J Thus'1 Mai at_11 Mwingi\I'Mfl” ,1...., .. . theret.iL.‘x1'|LL-is an average. L ofM' aboutin»! 253‘: inches\iTLi'ZC\ perpm year,you: at KatzeRd";' aboutchum: 23.1 inches,.m...‘~. and.Hni at.11 Ngomeni\gml. ' ‘ lessEC?“ thanK. '17 15J 5 inches.Hwho. DetailsDumflx ofm' rainfallHUMAN recordsr'ccm'd~ arcare givenmm inm the table11c l‘cimx.below.
RAINFALLRuxmm SmawmxSTATISTICS FORmm. THE:m MWINGI\I‘uzmq AREAMt" (Taken:Tukcw fromfrom the[he 1952I‘ISZ summarymmmmg reportvupm" oful' 1M;-the East|_;m African-\:';wc:1:'\ Meteorological\Iclcm‘uiugmai Department)Hep.
\A“_ IIL'L‘UHC‘L \xc‘L: .‘ Altitude-\Jmudc RainfallRLUHILM rainyELLI'lj monthlyHUHU‘:1_\ years animalannual
Siul'vnStation Mean “-35: No. of Heaviestmhm‘d‘l I , No. of I Average';:.“H.i'f I (feet) I 1952 I days, rainfall, recorded rainfall .1 LHJWLN ”:3 (inches) ,-- I I in in,,,,,, I 1952 1952 I I I \uI \w' Nzui\/'.x§ Dixrcnxm'xDispensary 2.5M! 23M" :‘uuunfcd 15'4“ 101H 21.4821-45 I I I Not I Nov.Apr.H“ KatzeKai/c DispensaryI.)wpc:‘~ur'_\ .. I 2.3m»2,500 I 22'61*.2H2: recorded4.3 I 15.48"34 I 10W I 23.19 \U\. Ngomeni\gumcm DispensaryDiapcmnr} .. 3.55“ H 5‘ 1‘ 42"." ' .. I 2,350 I 11'58 16 4'35 -- I 2,500 I 20-22 I 43 I ;;4 'Not\x‘l complete,Novembernot included.\‘L‘H‘Ju‘ (Jn‘uw‘Owing to the comparatively\uz'ulzwl} hm.low J'LZrainfall. mm:and Into fltheu: .‘M‘indigenous"mun practice:‘muttuc H"of mcrgrwovergrazing with\\ RH" both3!‘ :‘ cattlewith? and-r J, gnu»:goats theIhc vegetation\cgchumm isurn-.5111)mainly w.of the:hu WM»;thick thorn-bushIlmrri-m‘n type(Hm withxx . ‘h little:\.1|L' grass.mum. The lackbulk ofm' a 3mmgood cmc“cover ur'of vegetation,nugcuzlimw. asL‘A isEx cmcmuli}especially noticeablenmwcdbic inm nhumlmwdabandoned cultivated.miud patches,g‘dtd‘ca hm‘has led[ed 10to \L‘E'seriousi 5:“)egullying .mdand w'nHuuh.soil-wash, and11d wm:some L1"c.1«areas inm theHIC north-HUMM— westZdl'i‘are \C\L‘I'severely crm‘lcd.eroded. The'I E“: milsoil nowHum cm:covering:1"5 mostWm: Mof the'91;- wwgarea is.~ \1a red-brownred—m .m- wand}sandy mmtype and very deep in parts, but 01‘of poorwwr fertility.{Erwin}. It11 uumh‘i;consists mainlymummy \vI'of quart/quartz uandfl‘d 15m:iron undo.oxides, with a darker biotitic facies{Influx nearNew Evnlilc—z'wbiotite-richfi rocks.['m‘kx. THCThe tops[mm ofm“ Mumoni\Itmmm and;; L3 KyaikuyuK}'LHE\L1_\U (Gakuyu) have been gazettedmi axas forestMTV reservesmw‘ aw m1;and HIDthe ZULNtops cfof Muvaroa,\1 mu. ImbaiH‘3m.1:!dand MaiM Ll'areC forested; the natural virility1'» of\‘i' growthrumih coupledmur‘icd with\‘a 1M a.: slightly~115Mb higher rainfallMEN-Lt}! dueUm to7t- relief1m hashm' qua-1'00;covered Ihcwthese hillstx with\xiii‘. thick bushmm whiand inm somewmc places111mm mmwith trees. The w“)only recent{rum mapmu? m'of the1:1: mmarea isA thatI published.V‘.11“l.~1'L-J inH' 1940I‘d—H by the”1": aarmy, mon a1 \m'x-scale n5of 11':500,000'H (I(E.A.F..\.E . No.\n. M“.680, (jim'iwu.Garissa, 1945).THE. The111: Wangmap accompanying‘1 111'.»this reportTerm mmwas mm".-com- piled;‘1 from:.\:1'.;lcr1;ziaerial photos,g‘iwiw. uwmi'niic‘:controlled h}by a.1 <1'Q‘C1w‘f'skeleton ofMWtrigonometricalV'WtVrt‘L‘Lr'u; points surveyed by' the ,p"""'.
2
Survey Department, augmented by further points fixed by plane-table. The area was mapped between December 1950 and August 1951 as part of the systematic reconnaissance geological survey of the Colony. Mapping was made difficult by the heavy bush and soil cover which effectively conceals exposures in many parts of the area. In the higher and more densely populated parts in the west, paths and more varied relief enable the geology to be seen more easily, but in the low ground in the east exposures are poor..
II-PREVIOUS WORK . So far as is known the first geological reconnaissance of the Mwingi area was made by E E. Walker on behalf of the Colonial Office in 1902 (Walker, 1903)*. At Kibui (south- west of Kiormo ?) he found a hill of crystalline limestones, some of which he observed contained crystals of blue spinel, while other parts contained phlogopite and a yellow mineral suspected to be chondrodite. Associated with the limestones he found metacal- careolls'rocks rich in pyroxene and garnet. In the Pia (Tyaa ?) river he noted a cliff formed by another limestone, in which there were patches of milky opal and veins of quartz. Walker . .'dlriib\!d Mumoni and described it as composed of gneisses cut by common coarse-grained pegmatites containing magnetite crystals up to two inches across. He was unable to find imy valuable minerals in his traverses. Brown in 1904 travelled northwards from the region of Mwingi to Mumoni, and thence north-east to the Tseikuru district and the River Tana. He concerned himself mainly with geography, meteorology and ethnology and made little mention of rocks or minerals beyond stating that prospectors of the East Africa Syndicate had passed through the district, but had found no minerals there (Brown, 1906, p. 38) A rapid reconnaissance of the roads in the area was made by W. D. Harverson in 1934 (Mining and Geological Department, 1935) and short visits were paid by Dr. W. Pulfrey in 1942 and 1946. The latter noted the presence of ultra-basic rocks at Kamuthengi and the occurrence of recrystallized limestones at Nzui and in the north and west. He also examined the ochres formerly worked by E. G. Powell south-west of Nziu and south-west of Mutuangombe.
III-PHYSIOGRAPHYy I E I z H\\i() \.\ \l’EH The area can be divided into three physiographic units; the mountain masses of Mumoni and Muvaroa in the north-west, moderately high ground with residuals in the west, and a low peneplain in the north and east with scattered residuals (Fig. I). The country on the west has marked relief, the pattern of which is based partly on the predominant N-S strike and partly on the north-westerly trend of many of the rivers. It is a relic of a peneplain over 4,000 ft. high which now is most closely represented by the ground in the south-west corner of the area and by the summit levels of Kiormo, Ithumbi, Endui and Etinda. the remainder having been eroded considerably below its original level. The erosion surface is an extension of the bevel that passes under the base of the lavas of the Yatta plateau and which Schoeman (1948, p. 3) has suggested is the sub-Miocene peneplain. . In the north-west corner of the area Mumoni and Muvaroa attain a height of nearly 6,000 ft. and their summits are considered to be relics of the end-Cretaceous peneplain of Shackle- ton (1946, p. 2). From the base of Endui at 2,500 ft. approximately, the ground slopes away eastwards as a pediment with a gradient of about 50 ft. per mile, but in the eastern half of the area the lowlands slope eastwards at about 20 ft. per mile. The plain continues eastwards and north-eastwards to Garissa.\ and Wajir and has been referred to by Dixey (1948, p. 3) as the end-Tertiary peneplain. From this peneplain isolated monadnocks project as relics of the sub-Miocene peneplain. It is belived that the peneplains and their residuals developed by a process of scarp retreat and pedimentation. In the course of time the residuals on the end-Tertiary peneplain will be gradually removed by erosion, ultimately lewing a perfect plain. At the same time erosion will eat back into denuded remains of the sub-Miocene surface, gradually extending the end-Tertiary plain further west. The oldest surface in the area mapped can be traced only on the tops of the highest hills. Subse;:Juent to its mlturity, presumably towards the end of the Cretaceous period, there was a general rise of the land and another cycle of erosion began leading to the form1tion of a lower plain with residuals of the earlier surface standing up from it. This plain attained maturity in mid-Tertiary times. At the end of the Tertiary renewed uplift took place, when the older surfaces were tilted gently seawards and a new cycle of erosion and planation was initiated. The end- Tertiary peneplain resulted. ---.---- *References are quoted on p. 21.
L"o>- 354
There'I'J1c1'c areLU'C ulmtwtalmost no11:1 permanent[13112111112111 rivers,1'1112A‘. the111: drainage112111113141: consisting511119111511; predominantly111'c_111111111111:111_\‘ 111‘of water11:11:: L‘OLai‘coursesfics 1113.1that 0111).only-carryL‘JI'i‘} a;11‘1‘11ccsurface water11:11:1‘ 1111111;during 111:the rains:'.11;1\ 11."or for1116 11a short(E11111 tim~11111: afterwards.:11‘1c1’11 3111*. T.1cThe only111111 exceptionscwcpnnm toIn this111% are the{11c headwaters116111131‘4161" 111‘of 1116the Mwengo“1.101311 4110:and Ndatha\11111111 rivers1‘:1C1\ 11which111011 11%:rise L111on Mumoni\Iumuni and havelune a11 small\1‘11L111 permanent1161'111L111c11t 11511.1.flow, and :1a <1111I;11'_\solitary \‘w’springflg in111 the 11011bed 01‘of 1110the 1'11121'river Katzehave near11911: Etinda.Liinda. ThereT11c1'c1
0.30'5.
.UJ a .0017% .. co8 ...,3
fJ Etinda'O,- s-> 0 e
o'b ~ ~ ~ k“1‘lgean1 ~ @A~' (;)'b
t1 Mombui A A" ' @Q’n-HKUT“ " . ~tIKUY~‘\_/_ "1 '
\\ .\.
1.1"
L1.I C ,.,., .00 ~,.,., 1"00'5.
wRer'rr‘ar‘ s c‘ epd‘CVEt-SCC’CJS Peveuar m Remnants of end-Cretaceous Peneplain Remnants of sub Mocene Per1ep1atr: ~ Remnants of sub-Miocene Peneplain
‘ *_1 EndJerUa’f Pemeplar D1—'1‘ End-Tertiary Peneplain
Scale 01'1 5 10 15 Miles 1I L1 I1 4J
Fig.Hg. I.-Sketch1. 45kt‘lrh map of(11‘ theIhv chiefl'hivl‘ physiographicplusiugruphic unitsunih in1n the11w Mwingi\Iuingi area.aruzi. r
I 4I,
IV-SUMMARYIV -Sl'.\l.\l.\R\' ()FOF GEOLOGY
Thel he rocks 0;"of the tiredarea fallt'zill into three main groups: (1)it) metamorphic rocksreelw' belonging iiito the Basement S}Systemstem n!"of EastHist :Xt'i'tetiAfrica :iiitland prex’timetlpresumed toin hebe atof Archa:anArchie‘tti age.age, (It(2) post-Archa:anpm‘t— \t'chtel'i ultra-basictiltrtt—httsie intrusivell]ll‘Ll,\l\€ rocks inin ata plug tttat Kamuthengi,Kiit‘lllllltfitlgl‘ mattinwetlcomposed tll‘of tltiiiites.dunites, unnrthnxitex‘tihdanorthosites and serpentine,serpentine. associated with\tith ttitthriplnlliteanthophyllite andttitd magnesiteiiiztgite The Basement SystemSy All the rocksrock» exeeptexcept thethe marblesmtii'hlew crintttincontain ita high proportionpruimrtioii ut‘of Ltiix'ttltalkali felspar,l‘elxpur. much ut'of “hiehwhich probablyprohuhl} originated tix‘as materialilleti'iLIi introducedEiitrotiueed dtiiiitgduring gruiiitizutit’iii.granitization. Theillie felsparsllCl\D[1[\ tireare microcline,mi rticlins. t’it‘thoclttx‘e.orthoclase, perthitehei‘thite tmtiand wtlicsodic plagioclase,tiltigiuclzixe. \xliichwhich LIE'Care sometimeswmetimcs C\Cnl}evenly Cit»dis- seminateds izittted through the rocksreel“ zintland titat otherst‘liiCh irregularlyirregiilzirl) \egregtitetlsegregated iniii porphyroblasts,pnrph} mhltists. tittgen.augen, clots,dots; Kehliereiischlieren nror bands.Mimi» ’I‘heThe rocksrtielxx containing them might whenoften behe termed migmatites,mlgtltztiilcx whichuhicli havehuxe beenheeit detiiietldefined byh) TurnerTutner (1949,il‘ti‘r). p.h. 11)ll) asLi\ “ctimpmite"composite rocksreel“ in \thichwhich the effectsetl‘eetx nJ‘of tiietttttiorphismmetamorphism havehti\e been Ct,‘l‘t‘.',‘llle\llCLlcomplicated h}by makingsoaking atof rocks iniii migmaticmigmzitic llUlkl.fluid, o:‘or h}by the dexelopmeiitdevelopment 0tof lenticleslCIiliL‘lC\ tintland \heetssheets nt‘of litiuitlliquid mtigiiiaimagma. . . .". AeenrtliiigAccording to this \iCllnilidefinitionfill allLlli the Basement SystemSytem rocksruelxs ut'of the their.area, eweptexcept the limestoneslii'iiestuiies Llllxland possiblypusxihl) the other L’iliL‘iil‘L‘UllN’calcareous l‘tiCh\rocks, euuldcould hebe eltix‘xitietlclassified ti SumetimeSometime Litterafter their dehmitiundeposition the Basement SyiemSystem roeimrocks were foldeduntied. tiritland iliultetlfaulted Llllkiand intenselyiiitensel} plane-foliatedhittne—fnlititetl parallel,mruilel. it I\is helzetetLbelieved, toin the tit-igziitiloriginal i‘CtlLllIl‘g-Dlilnci,bedding-planes. The strikeStrike 05‘of the foliationlt‘lldllt‘l‘t isi\ regular:‘egtiltir itittland rtiii>runs generallygCIlL‘i'Ltll} north-southitn:'tli~.~.i;ttli with Lta gi'tttltittlgradual north-eastNorth-east swingwing in the north.mirth. 'l‘heThe tlipx‘dips ofat the foliationi‘nlitttiun tireare variable,\iiritihle. cluedue to foldingtlilditig and the super- impositionimpmitiuii nt‘miiitii‘of minor foldst‘tiltlx' mittand eositm‘tinm.contortions. The metamorphismniezitittnrphixii im‘mx'ctiimposed during the folding was augmented ':)_\by graniti/tttinii.granitization. There isH noiin intltetitiiiiiindication that the rocks or t‘;ii‘t\‘parts titof them bxamehictttite completelycompletel) molten duringtttii'iii; thistits process,pt'ncesx. butl‘Ltl there i>is evidenceexttleiiee iiiin the coiitnrttiiiiscontortions and flowtime strtiettiresstructures that theythe} becameheettitte plastic.plihlle‘i Itlt ttiiiistiixappears totn tLiethe \\l‘llC|‘writer that \\ltCllwhen the}they were in thattl’ut statesttite theythe} werehere etiitiprcascticompressed roundi‘titiriti thet‘i: melanocraticmclm ici'titi ‘JtlietIHCiV-eil'glliLlCCt‘LHcalcareo-argillaceous hiutda.bands, whichtilt-aeh remainedremtuiietl stiiidsolid and were t'nltletlfolded .tt‘xiand hrnlxeii.broken. Sometime afteralter the metamorphismiiietttziixiriihixm ofhi the BasementBux‘emsiit S}\[Cjil.System, it uttx‘was injectediiiiecteel byhi tiltrtt-ultra- basicljzix’ie plugs attit Kamuthengi.Ktitii'titlieiigi, Sincehinge thattltttt time thetie areatire: hashtix beenheeii heavilyhemilj. erodedermletl :iiiiand levelledEe\el’e_i duringtittr'itig successive\ticces’s’he periodsperittilx ofnt' peneplanation,iieite'iltirtitini; endingeiitln‘" withmil: thell‘.-._‘ presenttireaeitt tut}day topography.ttmngrttph}. TheTl‘e areaarm is39 nowmm coveredemeretl mainlytl‘t'tll‘ by_» red-brownred-h an sandy«.tntlj. soils:\‘lixi similarwittlui soilsTwilliN havell;l\C beenl‘eei: et'it'reltttet':correlated at:tt Malindi\I'dillhii tel.(c.r. Thompson,Tllt‘ltttixtfllh 1956,i‘-I:h_ p.pt ht)30) with PleistocenePie‘ixit‘CCliC andtiiitl RecentRegeiii CtklNiLlicoastal ticpnsitedeposits. --~~--- - 5 V-DETAILSV—I)F..T.»\ll..S OF GEOLOGY 1.1. Basement System The rocks olof the Basement SvsiemSystem can hebe petrographicallypt:ttogi'L'tpliic'Ltlly di\ideddivided into numerous types which are descri'lieddescribed helo11=ttndL"1below under thLthe l0llo11'ingfollowing groupsiegroups:- (I)(l) crystallineci'ystaliine limestones 12}(2) calc—silicatecalc-silicate rocks (3}(3) pelitic rocks (4){4} semi—peliticsemi-pelitic rocks (5)15} psammiticpsamnfiitic rocks TherThe mappingmappi 11g was insufficientlyinst: Lciently det'detailed:LIledtto enable11Lte the working out of a complete strati—strati- graphical succession.succession, but it appears from the specsequence11c ice eltislestablished1ed inIn the south—south-westwest partpart o!of the area that it is broadly as follows:-l‘ollo11-s2W Feet{“L‘L’f lnterhandedInterbanded psanuniticpsammitic granulitesandgranulites and semi—semi-pelitic—pclitic gtgneisses.neisses... 8.5008,500 Semi-pelitic gncisses.gneisses, probably with part passing into pelitic gneisses in the north-westnorth~\1'cst 1. L. . . . 1 . 1 34.00024,000 Crystalline limestones and semi—peliticsemi-pelitic gneissesgneisses. 1 . . ., 10,000ltl.ll(l(l {(?)'.'] (I)[ll Crystalline(‘1'.1'1'1’111’1'5119 linn’stoneslimestones occur as isolated lenses or lines ol‘of lenses mainly in the south- \1LstLiwesternn anLLand no:northernthcrn parts ol‘of the 'LLre'LL1I‘L-1os1area. Most ol‘of the lenses are EU50 to I0!)100yards wide and they vanvary1-' in lennthlength from a quartetquarter L"i|of a mile to tantwo miles1miles. The lens at Gahie.Gahie, in the centre 01‘of the meat.area, is both solitary and e\ceptionalexceptional in sixe.size, as it is Still500 yards wide and nearly three miles long. The soil merlyingoverlying the limestone handsbands is muchmach whiter than that resting on the gneissesgneisscs ol‘of the remainder ot‘of the area and contains superficialsuperficial limestone nodules,nodules. while the bushhush cover is greener but more stunted and open. The limestoncslimestones var}vary l'romfrom fifine-grainedne—grained sacclLaroiLlalsaccharoidal marbles loto cL'Jarse~grainedcoarse-grained roclLsrocks, though most have a grain siiesize ol‘of about a quarter of an inch. They consist ol‘of grangranularLilai 11mosaicsosaics oiof grains ol‘of eL'ucarbonatehonate with prominent rhomhohcdralrhombohedral cleavages and twinning.twinning, with pink and white calcite and dolomite in proportions varying from nearly pure calcite tin(in specimen 4545/180,{Ht}. Galui hill!hill) to nearly pure dolomite (in specimen 4545/143,143. from the lens near the southwestsouth-west corner ol‘of the area].area), as estimated from the reaction of‘of crushed material in cold dilute hydrochloric acid. By using Lemberg'sLemhcrg's test tHatch(Hatch and Rastall,Rastall. 1951}.1950, p. 322,!322) it was proved that in marbles ol‘of inteninter- mediate composition grains ol‘of dolomite and calcite Lu'eare e1LL1l}i11te1111i\eLl.evenly intermixed. Scattered sparsely in this mosaic are Lariahlcvariable amounts of lil11c»hearinglime-bearing allLali—alLiniinousalkali-aluminous minerals represented byh} calcic plagioclase or scapolite.scapolite, inuscot'ite.muscovite, epidote.epidote, and ferromagnesianI‘erromagnesian minerals represented by Lliopside.diopside, hornblende.hornblende, l‘orsterite.forsterite, and serpentine and chlorite.chlorite, the magnesium havinghating been provided by dedolomitization ol‘of the limestone,limestone. The limestone lenses are also sheathed by and sometimes intercalatcdintercalated with rocks composed ol‘of calc—silicatecalc-silicate minerals formed b}:by the ClCL‘lolotttlti/‘Ltlitmdedolomitization (iiof the limestone by reaction with silica~bearingsilica-bearing minerals inin. surrounding or included sedimentssediments. In some instances.instances, ho'LLeL-er.however, recrystallizedrecr} stallized calcite is in passive contact with quartz.quartz, as in specimen 31545/]48148 from the limestone handband on the road just east ol‘of the River Tyaa.Tyaa, \1'l1ereawhere a recrystallizedrccrystalli7cd limestone encloses unaltered quart/quartz grains.grains, and where some of the limestones have not been completely surrounded by aLL protective sheath of calc-silicatccalc-silicate minerals. Lack ol‘of espisin'esexpDsures prevented a determination ol‘of the widths ol‘of the calc—silicatecalc-silicate sheaths and their passage into graniti/edgranitized rocks. (2) '17::-The 1'Lii'L'—.si‘li’r'c.rn'calc-silicate rocks are usually meson1esot_1-'petype and l‘oliatc-Li.foliated, and in addition to their occurrence round the borders of the limestone lenseslenses, or as b-Lndsbands within thethem,m LitheyC}.- some—some- times toimform extensions to the limestone lenses.lenses, interdigitating.nrc1dtrviLLLLaI 11iihwith the surrounding sedi—sedi- ments. Calc—Calc-silicatesilicate rocks not associated 1.1.itl1with limestoncslimestones are also seen in small isolated bands andand lenses in other parts ol‘of the area.area, the largest beingbeing onon Muvaroah-luvaroa and north—eastnorth-east 11.“of Gal.Gai. The most commoncommon minerals in the calc—silicatecalc-silicate rocks areare pale—greenpale-green to green faintl}.faintly pleochroicpleochroie diopside.diopside, deep-green to brown hornblende that appears to be secondary after diopside.diopside, pale—colouredpale-coloured epiLloteepidote and clinozoisite.clinozoisite, plagioclase of lahraLlorite-hyto11-11itelabradorite-bytownite com—com- position.position, scapolite.scapolite, often quite large crystals of sphene.sphene, and small sub—hedralsub-hedral crystalscrystals Lil‘of hrownbrown garnet. Quartz.Quartz, orthoclasc.orthoclase, microcline.microcline, apatite and zircon appear in less calcareous examples, which have probably suffered some granitizatinn.granitization. ~J 6 Some idea ofiii the variation\ariziiinn orof the cede-silicatecalc-silicate rocks is obtained from thcthe following esti—esti- mated volumetric\0lL1fllCII'lC modes. 45/12245123 ~1545/12413—1 45/141451% 45/161451(il 45/16745 I67 45/17175171 45/176715176 % % % % % % % PlagioclasePlttgioclttsc ... , ... . 30 30 30 5" 10it) 15IE 20it] DiopsideDiopsidc .., .., _ 303U - 40 65(i5 25 8t‘ -7 HornblendeHoi‘nblcndc .._. .. 12I: 35 30 7T -777 -7 + ("Ii11010isitc—epidtttcClinozoisite-epidote .., i 6(v 35*5 -77 31 40 12I: 35 ScapoliteSuzipolitc ... , ... . - -7 - 151'? 15l5 20:0 10It) Quarv.Quartz.. t ...... 20It") - - 2I -7 7 30 30St) Sphene .. ..V . 2 -7 7 -7 7 3a 10It) + 21 Garnet .., ..i , -7 -77 I -77 - - 151" 3 45/12245 122 On()n pathptith to Imba,lmbt‘t. justjih‘t north of the NziuV/Eti river.i‘iwr. BordersBi\i‘ilti\' aLl limestonelimcstiinc lens.Sum. 4. 45/124‘15 1271:“As 44/122.44 ill. 45/1417‘75 Hi FromHum thethc valley\Llllt‘} southSULllll oftil‘ thethe. GarissaCidi'mii road:‘utid nearnc;ii‘ thethc bench-mark,hench—nuii'k. south\L‘Ulll oful' Kiormo. Ai7\ calcareousCLllC;ll'CULl'\ gneiss.gncis<. 45/1617151M Mutui\ltitiii hill. 45/16745 [67 Kandaonikfiittlt'itiiii RidgeRidgc neartiCt’ii‘ Katze.kttt/C. Floatl'lULtI block.black 45/17145 [7] Fromh‘nm limestonellIIICNLUIEL‘ bandbuild onUH roadmud abouttihutst three[lHCC mileslflllCS southwutli ofml Katze.hut/Ci 45/176715 176011On road,i‘mttl. oneiiitc mile northiitit‘tlt ofol‘ (izii,Gai. Specimen 45/140,715 MD. from the Garissa(,i;ti‘i<\';i roadroitti southmtith of(‘l‘ Kiormo,Kinrniii. containsCtlnlillll\ Lihtmdtiiitabundant crptulx'crystals ofUl\ brownhi‘tmn biotitehittlile associatedLlNNOClLllL‘tl with\\l[ll largelttrgc poikiloblastictmilxiiuhltixlic grainsgi‘tiziix oful‘ pale-greenpiile7gi‘ccn pyroxene,1W} 1'0\C[‘.C. gi'cengreen hornblende,hnz‘nhlendci splicnc.sphene, large grainsgrttim oft‘l‘LIDHIlIC.apatite, tia perthitic felsparl'clsptii‘ and quartzquartz. Specimen 71545/164,16$. fromfrom the amphiboliteumphihnlitc lenslcng neartiCLii‘ Kyando,K};liltl0. is15 ita lime-richlimo-rich rock composedmiiimwcti n!of nearlyHtill'l} cqutilequal proportionshmpni‘tinns‘ ofmi diopsidediopwdc andiind hornblendehnrnhlcndc with\xith lesslC\\'Il1;iI‘:than fivell\CP:l‘CCHEper cent oful'intci'xtitizilinterstitial plagioclase.[‘lnIt‘ClLHfi The rock is similar\i‘il‘tllul’ to one0116 described byh} Bear 11952.(1952, p.n 1l II)l from{ruin the western\\C\ECI'H Sldcside of Mumoni south\U'tllli of Muguthu,Miigtithii. and forms[\OI‘IIN part of antone miof aL1 number of isolated,1\‘0lillC\l. usually'tl\'Ll(ill) CUE‘ICOI'tlAHlE.concordant, lenseslcnscs occurring betweenhchwcn Muvaroa\Iiniiron ontin Mumoni\‘ltltflOfli and ati pointpaint wtithsouth ofnl‘ Kyando.Kyiiidix Slll'lllill'Similar lenses occur furtherlin‘thcr muthsouth at MukuniMtikiini Lindand Kitumbi.KliLlIlll‘li The lenseslcn~cx are notnut liCi'chere d\\UL.'lLllC\lassociated \\itliwith anyL111} otherUllltfl‘ calc-silicateculc7sslicute rocksrockx buthut in central Kituil\llLIl similar\iniiltti' rocksincl“ havehtixc beenhccn mapped tix’as melan-iiiclttn7 ocraticUCI'flIlC facieslttL‘lCS ul‘of more normal calc-silicateCLt7>lliCttIC' rocksincl“ (Sanders,(Stli‘tdCI'\ 1954,lLE-lt p. 10).10}. (3)(Rb PeliticPt'i’i'ii'i- rockslilt'y'l\\ are representedI‘C[WI'C‘,\€I]§Ctl inin the areaiiI'L’Ll byh} smallsiniill bands,l7;tlltl\ schlieren,\chlicrcn. clots and lensesEcnscs inin thetlic semi-peliticscnii7pclitic biotitehit’wtitc gneisses,gneiswx andLtIlLl locallylocull; byh) rocksweb with gtirnctgarnet tintland sillimanite.\illizimnitc. TheThc sillimaniteKillimunitc always{1l\\'d_\‘§ outir IIiiii PlateHair I| :I (a){Lil View\ its“ southHUIIIh fromfrom Gai(.'-.1i showing«.Ilzminu peneplains.|)L‘IIL'|I|:Iil]\. (b){In Leucocratic1.i‘l|{'nl'l;l[il: biotiteIsintitc gneissfinish». enclosingI melanocraticnucrnlir masses.mama. "I 111 ---- 1 I .u 8 PlatePlan: JlH (a)1m Leucocraticlxucncmtic biotitehimim gnt‘is\gneiss rnclnsim;enclosing I‘nldcdfolded nu'Lmsu‘rLzlicmelanocratic bands.hundx. (b)Ihl Melanocratic\lchlnm'mtic biotite-richhimilgurivh band,hum]. bent and injectediniwml byh) quartzo-felspathicq1mrl/u-flpzlthic material.mulrriul. ~ - 9 SpeeimenSpecimen =1545/7 is composed mainly ol‘of gneissiegneissic quartz and a little orthoclase.orthoclase, with the foliationl'oliation planes marked bby‘ many ettsileasily-weathered—\yet1tltei‘ed iibresfibres and thin bandshands ol‘of .‘sillimanile.sillimanite. The Ltuatquartz-sillimanitetz—sillititanite roelLrock represented by specimen 4545/160I60 was loundfound only as L1a tlnatfloat block. It is a txltilcwhite and schistose rock that in thin section is seen to be composed o-'of L1ua‘.tt7quartz, site‘Loessheaves L1l'silli1nanite.of sillimanite, and secondary sphene. (-'i}(4) Thethe semi-peliticwand—119.. t‘ gneisses:rrtt'isst's forml‘orm a variable graititi/etlgranitized and ntetainorpliosedmetamorphosed series and in places havel1a\e nearly flatllai foliationl'oliatiL‘in planes.planes, while in others the foliationi‘oli‘Lttiost is highly contort-Ltdcontorted and cut h‘s-by numerousttuittet‘otis minor Ct‘nss—cross-fractures.l‘rttL't‘Lires. The country formed"formed by the semi—semi-peliticpelitie rocks1‘1 is usually-usually low-lyinglon—h-‘iitg and soil—soil-covered,entered but1111 the:there‘e are oecasionaloccasional hills and lL11\‘\L11L11L.‘11L\slow whale-backs. The whale-backs\\l1L1lL.-lJLlL.‘§\S usually oeL‘Ln‘occur where the rocks are well banded,ban-Lied. when theyihe_' Ltiea.s‘L1oltL1‘.are also often highly contorted and ply-‘gtnalieallyptygmatically l'olde‘Ll.folded. The rocks can behe diyitleddivided into seter‘Ltlseveral typeslypes 1111.on their L‘olotn‘colour i11-Lle\.index, amount and type ol‘of granitirationgranitization and on theit‘their mineral e1‘1111positinns.compositions, but the series is so \at‘iahlevariable that seyei'alseveral such rock-typesrock—types may hebe seen in one euros-Lire.exposure. Due to this and to the limited time a\‘aiE'Ltbleavailable for the sui‘Ley-survey it \\wasas impossible to map diyisionsdivisions in the group. The main rock types are: biotilebiotite gneiss‘es‘gneisses and h11r11hlende-plagioel‘asehornblende-plagioclase gneisses.gneisses, L\:thwith transitionaryEransitionary hornhlende—biotitehornblende-biotite gneisses. Biotite gneissesgneisses in the tntl1u—l\'le1‘uEmbu-Meru 'Lireziarea haxehave been well describeddescribed by Schoeniai:Schoeman i'l'JSJ.(1951, pp. [313-16)lL'1} under thethe heading L‘1lof titieinatites.migmatites, andand lromfrom southsouth-east-eas‘t l.1nl111Embu by RBear ll;11(1952,fi p. l12).' They are1'1re composedcomposed olof L111at‘t7.quartz, plagioelaseplagioclase, potash ielsparfelspar andand hintitebiotite 111111with :1LLes‘so1yaccessory apatiteapatite, sphenesphene, /.1i‘L‘1111zircon and ironiroit or‘eore \\i|.l11with rarrerarer,. more sporadic.sporadic, rutile and museoxite.muscovite. inTn some L\7ex- posures garnet 11'wasas lL1L111-Ll.|"11efound. The L‘1L1'Lu‘t/quartz andand l‘elsparfelspar 1'(which\\ hieh ha\ehave deLelopeddeveloped partly asas products ol'of graniti/aliontgranitization) harmform a gt‘an'LilL‘1segranulose g1‘L‘1L1nd11111ssgroundmass inin the I'UCiKS.rocks, asas in specimenspecimen 4545/133[33 l'romfrom the 1111tnorth part ol‘of the central rib orof Ithumbi,lt'nurn‘oi. but the ielsparsfelspars also limitform T‘Ltf])l‘1:\l'tll1litnl5porphyroblasts {as(as in specimen 4S45/231‘1 from the summit ridge ol'of lthumbil.Ithumbi), angen.augen, ‘L‘hschlieren,lieten bands or peetnatitcpegmatite- like \‘einsveins his(as in specimenspecimen ~1545/3.‘1 from near WallaWaita dam}.dam). The \'Lveinsins‘ lolloLLfollow the toliationfoliation planes and the minor c1‘oss~l‘t‘aetures.cross-fractures. In the larger Lentsveins the L'iy-‘stalscrystal sizeie/ is much L‘L1a1s‘ercoarser andand mag-mag— netite and biotite are sontL'Limessometimes present in crystalscrystals up to tln‘three eentintenescentimetres across. A.1‘\ common l‘eatui‘efeature in the leLiL‘L‘iL‘ratieleucocratic L‘11‘or mesotypetltes'1[}pc gnei‘sse‘sgneisses is the inclusion L11”of irregular but sharply dedefinedfined melanoeraliemelanocratic portions round which the host—rockhost-rock has flowedllnued and become highly contorted. The dark inclusions are sometimes composed entirely-entirely 111'of L‘l:.1L1‘lL—b1‘o\s11.dark-brown biotite in interweavingintern-eating flakesllalxes or of l1iL-1‘1itebiotite and hornblende or 111‘of hornblendeht ‘1ble11de alone.alone, but they usually contain plagioelaseplagioclase and potash felsparlelspar in addition. They are arranged parallel to and along planes \\whosehose traces in outcrops followl‘ollou and indicate the general structure. Inin the banded types the l1bandsands sometimesometimess taper laterallylaterally, but are often displaced by sm'tllsmall l‘aultsfaults or even sharply terminated. TheirIl1ei1 L‘l1L11L1ete1‘istiescharacteristics suggest that tlte‘t‘rthey represent more calcareous or argillaceous bands that were metamorphosed.metamorphosed, distorted Lin-LLand brokenbrolLL-n diningduring foldinglolding and sometimes partly digested during1during granitization.et‘anitization. Hornblende-biotitellornblende—hiotite gneigneissessses and hornblende-plagioclasellt’ll‘lllFlEIldEeplilglUCl’Lhfi gneisses representing more calcaretcalcareous1s members 111'of the sesemi-peliticLini——pelitiL‘ group havehaye been described by SeltoemanSchoeman tl‘Mb‘.(1948, p. 14,l4. Kitui,Kilui, and 1951,l'Jil, p. 10,ltl Embu-Meru)hnl1n-.\-le1‘n_1andand by Bear 1195:(1952, p. 13,1.1.sout'11—eastsouth-east Embu).tntbui. Inin addition to the presence or predominance (1|of hornblendel1o111l1lende among the dark minerals such rocks are characteriyedcharacterized by a marked sparsity-sparsity ol~of potash felspar,l'elspai‘. especially iiiicroeline.microcline, \Lhicl‘iwhich suggests that they havehate not been gz‘aniti/edgranitized as much as the other 1ytypes.pes. N‘ltsseotileMuscovite oeeurs‘occurs sporadicsporadically :11in ‘.L1"L1LLsvarious i‘LiLlL‘srocks throughout the area.area, but is present in quantity in a quart/rm.use-oyitequartz-muscovite sLhistschist at Kaikuyu lt:ll.hill. S]1L.‘i-.nenSpecimen 4:145/78 from t-that locality is comp-.sedcomposed entirely ol'of \L-ell~s‘oliztte1iwell-foliated c171arse—1-1LLine-Llcoarse-grained Litartxquartz \Lithwith oceaoccasional1nal "elspat‘sfelspars and muscovitemuseot ite in flakes.flakes, thin folia,E‘olia. bandshands and lense.lenses. 011On the flanksflanks 111‘of the l1.'"|lhill the muse-mmuscoviteite is :Lssoeiatedassociated with biotite and 111‘farther12." away the rock passes:passes into L1a hintitebiotite gneis‘s‘.gneiss. [5'1(5) PsammiticPs'rmmntit' gneissesL’Hdmtl’a menoccur as handsbands or lenses :11at numenumerousrotis places =.hr-L1ug"1ontthroughout the .1area,tea. \1whereltLte they sometmtessometimes form highiigh ridges S'lCllsuch L1sas Endui,1r.ndt1i. \‘luiMai Lindand \"lilxogu.Mukogu, but more usually forml'ot‘n1 low but prominent cragg\craggy features. The predominantpt‘eLlL‘Ln‘tinant rocki'oek type is a Liquartz-felspar‘/.~l‘elsp'L1=‘ granulite1rantilite which weathers into rounded boulders with Lia ehcharacteristicat‘acter istie lawnfawn wincolour:‘1 spotted 11yby scatteredscattered, sub—hedral,sub-hedral, black magnetite g1L1i11s.grains. They-They are similar to granttlitesgranulites Liesetibeddescribed by Shackleton 1'1941’1.(1946, p. 12}12) froml‘1‘om the Matthews.\-‘latthews range and l1_\.-'by Bear 1(1952,WEI. p.11.. 18118) I‘romfrom south-east Embu,l‘mbu. being composedeomnos‘ed of quartz.quartz, microcline,ntierocline. and Oligoelase.oligoclase, with suhh‘edralsubhedral titanithroats—magnetite.titaniferous-magnetite, and oeeoccasionalstonttl flakes of muscovitemttseoL-‘ite and biotite lyinglying1 parallel to the faint foliation.l‘oliation. As already mentioned some are spotted by a few garnets. ~ 10l O 2. Pleistocene and Recent Over(her most ofol‘ the Lll‘e'darea and especially on the end-Tertiaryend—Tertiary peneplain,pcncpliiin. there Lireare red-bro“red-brownn quartzosetitlai'txosc soils such as:15 CD\CI'cover large areasLll'CZii of East Africa»\l‘rie;i iintland arelll'C Sltl‘lllill‘similar to soils thutthat havehtue been correlated with Pleistocene sands near MalindiMalinth tThonmsmt.(Thompson, 1956,1956. p. 30),30). There are UCCaSlt‘l‘léiloccasional developmentstlexelispmenis tilof Surllieesurface limestone tiittland lateriticltttei'itie ii'C\h~ltotie.ironstone, \ihilewhile \\wherehere Lll'éllllédrainagege has been hindered or confinedettitllned there are black cotton mils.soils, helutibelow \xhiehwhich there aretire mmetimes'sometimes restricted deposits atof gypsumgnxum andLind uehreuusochreous emu.clays. Some bandshciiid> initi the valleytulle} Sellssoils that apparently haveham :1a high content tilof mluhlesoluble Hiltssalts uiLare used.used by cattle a1 3. Intrusiveslntrusiws .... The intrusiveintrume rocksl'tlxN ennx‘ix'tconsist ul'of pegmatitespegiiiutite‘ which\xhieh veinmin the BasementHuRement SystemS} lli(1) PEGMAl’ttAHiiiiSTITES 'l'lteThe pegmatitespfgillitllli‘x viof the Basement SnteinSystem eeeuroccur as;1\ numerousnumerou< ~m;illsmall wneurdaniconcordant and d!»dis- cordanteordunt veins.\eini. TheyThe} are composedeompmetl oftil ait coarse-grainedL‘t‘lll"!*§3'lilll€tl mosaicmimiie oful‘qutirt/quartz andtiinl potashpntuxh felsparsl‘elx‘piirx with\\ilh occasional('VL’L‘11\lUl‘i;ll crystalser} Killlx‘ ol‘of biotite,hintile. muscovite,miisemiie. amphiboleuntii‘nihule ttlitland titaniferoustiiuiul‘eroug magnetite. ThelltC veins\Cllt\ oftennlten followl‘nlltm fracture:‘ruetuz'e planesplauiex tuttiand were probablyhmhuhl} formed Litat tia latelute \tn'stage in the meta-meta, morphism.morpl'zism, AnXi exceptionaleweptiunul graphicemphie pegmatitepegmutite composedemnpmed onlynnh tilof uii;irt/quartz gt‘dplile‘nll)graphically inter- growngrmxn with\\l1l‘l microclinetiiiei‘oeléne was\\;l\' foundlt’itiliti westnest ofml Kyaikuyu.K};iikii_\ii. Itli hiix'has .ia largeltiree eventextent Lllltland LLDDCLII'Rappears into havenine a:1 ermveiiltingcross-cutting relationshipi‘elzititiiix'l in to the country-rocks.UHL]ll[l'_\-t‘t‘cl\\fl (2)ill ULTRA-BASICLi ii< t~R\\:( INTRUSIONSl\ i RL \li .\\ Thelhe ultra-basicLilll'Ll’l‘rzlSie‘ intrusionsintrusmnx‘ lie closeelme tiigethei‘together in the easterneux‘tersi hurtpart tilof the ureaarea :iittland e‘tiliconsistfilxl of:- iii!(a) the hill Kamuthengi;Kitittiitiiengi; (hi(b) :1a lowlim unnameq.unnamed hill,hill smiifisouth ul'of Kamuthengilxuinuthengi LlllLland ju - ... -~----~ '" I ~ ~' ------N .- .- _ ‘. P M .n m a u, .. u u n. m w. . A M m .y .L m u 1. . I t P h M , w 2 ‘ m m w 3 ._ w C. ‘ .n k r a an m w M .4. w n 0 x . a cc A H n. a s. n n. (.1 .. _ x ‘ V .v .w , .r o a 1 d _‘ .J rm C D 0 JOOH. 600 900 f200 FPOt , AApp,o"m".w 'cmmae \‘m!".Ie uin Myfeel r‘.,., ‘mu‘ ln 4.1 11-“ Mum .AIIi'"") “3‘ Fo'm-lin" .t 4()-fool'""mf, .l’iu.Fig. 2.-—-(.'uulugicul2.-Geological sketch map 01'of KaunuthcnuiKamuthengi hill. I I~ 12l n tit(i) Dunites.-f)1(l1[tt’\.—Tl1CSCThese roeksrocks are nowno“ mainly composed t‘it‘netinoliteof actinolite LlHCland ehloritechlorite with \Ltriathl}variably serpentini/etlserpentinized untland o\'i\h'/-:tloxidized remnants of oli\ine.olivine. The)They are t_\pilietltypified h}by x'peeimenspecimen 3.545/101,101, which in the hand-specimenhand—Rpee‘tmen is green and finelytinely mietteeousmicaceous \\ithwith scattered.scattered, Suh—sub- t‘tngulttrangular hrmxnbrown spots of serpentinized C‘ll\lti€olivine tl-‘igi(Fig. Tutti3a). Specimens 4545/118I18 and 4545/3939 are similar. InIn 2!a thin section 01'of speeimenspecimen 4545/101lOl the brownl‘t‘oun areas are seen to behe eomnmedcomposed ot'of limonite-stainedlin‘tonite—stttinetl serpentine.serpentine, hone}honeycombedeomhetl h}by «mallsmall \elm'veins ol'of eitleritetchlorite. Remnants ol‘of olivine are present in the pseudomorphs and war)vary greatl)greatly in numberttinther and «We.size. Between the ser—ser- pentinizedpentiniied grains there is {1a mass of pale-greenpale—green aetinoliteactinolite and pale—greenpale-green elinoehloreclinochlore ecrystalsluls with 21a small amount of iron oreore. The tietinoliteactinolite is in bladed er}crystalsstttl< ol'of \variableLtritihle ~21:size amountedassociated with plates ol“of the ehloritechlorite set with various orientations. The tietinolite—ehlot'iteactinolite-chlorite aggregate in part simulates flowilou stt'tiettirexstructures round the $e’t‘pentini/etlserpentinized massesmax‘sex‘ so that it EIDDC‘dHappears to havehme ...~ penetrated and broken apart the original oli\olivineine musg.mass, rather than toto hatxehave been derixedderived frontfrom the oiixineolivine byhy alteration in situ.trim. The \tit‘itttionvariation in composition of the dunltex‘dunites isi3 Rl'tout‘:shown h)by the followingl‘ollmxing table ol‘ex‘tintzttetiof estimated volumetric\oltimetrie Ult‘LlC‘N'Imodes:- ~1545/]0110] 45/39‘15 EU 451MB45/118 % % % ()Ji\ineOlivine and olivineL‘llHllC pseudomorphspseudomorphx‘ .. 353‘ 25 bit60 Chlorite .. 343—? —.~ It)29 73 \ ActinoliteAetittolite .. .. 3t)30 { ‘ )J 101U Iron DreOre .. .. 1 2I 1l The eltloriteqnxinolitechlorite-actinolite tlunitedunite predominatespredomittatex‘ in the lowerloner slopes ol‘of Kamuthengilxunttithengi and in the north and east spurs,spurs. where\\ here it is15 uppgtreittl}apparently vertically\ertiettll} jointed.jointed along bearingshearing; of 1110°ill and St}80°.. Itlt appeai‘xappears to formterm the ULIICI'outer or lower portion of the complexcomplex. A completely altered dunitetltinite isis representedt‘epi‘exentetl byh)‘ specimen\‘peeimen 4545/111,lll. which consistseuttsixtS largelylurgel} ofot‘ massesmisses ofol‘ fibrouslll‘l’nth crystalser) stulx thatthin are probablyprohtthl} amphibole,umpltihole. interspersed with\xith limonite grains.grainx AggregatesAggregate» ofol‘ plates ofoi‘ chloriteehlorite and smallSt‘ttlll massesntttsxe; ofot' carbonateeurbonate liehe interstitiallyinzerx‘titittll} to the amphiboleamphihole clusters. Another variation,\tiritttiotr of01' which onlyonl} :1a small amount was\\L].\' found,l‘oiintl. Consistsconsists ofol‘ chloriteehlorite inIn \\hiehwhich lie scatteredsetttteretl smallsmull prismaticpi‘imtzttie erytgtlscrystals of hornblende.hornhletttle, .... Fig. 3.-Diagrammatic3.—[)iagrammzitie microscope drawings,drawings of thin sections of rocks from Kamnthengi.Kantuthengi. (a)lat Altered dunite.dnnite, specimen 4S45/101,10L xIS,\lx. ordinary lightelight. Heavylit-my lines‘lines = aetinulite:actinolite; linefine line».lines =7 ehlurite:chlorite; black representsrepresents hrtmnbrown ~t'rpentineserpentine which is minedveined by ehlnrite.chlorite. 1t(b) Plagioclase-bearingPlagioelttse-h“.trint,y dunite.dnnite, specimen 4545/102,102. \20.x20, ordinary light.light. Crystals of uliiineolivine are surroundedsurronnded by mm",zones of urthnmorthopyroxenern\(-ne and uetintactinolite.flite. Plagioclasel’lugitmltts’e occurs tnin lntt‘r's‘tlfl'dlinterstitial punlstpools. ~ -' ~~"""-~ ~ 13 ThereTIICI'C isix Iia CL‘IIIIIIIcertain amountIImOLInI 03'of SCI._II'Lsegregation‘LII Iion and oi'iL‘nIaIEIInorientation III‘of theIhe LIIII‘Ixdark IiIinCi‘IIIx:minerals in IIICthe II dunites.IIIII‘IIICx. ThisI'IIIx isix seenSCCII inin theIIIC parallelismIlliI'LIIIL‘IISEI‘I ofLII largerEIIIgCI melanocraticnICIIinIICI'LIIiL“ lensesiCIIxCx andLIIILI bands,I‘LIIILIx in theIII:- strongwrung foliationI‘LIII‘IIIIIIII ofIII" the[I7C darkLI'III‘II' mineralsminL-I'aix' inIn suchxiich bands‘IWLIIIIIx andLLHLI inII‘. theIIICIfeebleCCIIIC alignmentiIIILInnIL‘nI ofIII darkLIIII‘ Ix flakesII =I'x'L‘.x CllHIand spotsmum in theII'IC morenILII'L‘ felspathicI'CIx'IIzIIIIiL' portions.pIII'IiIIIIx. (ii)Iii) Plagioclase-bearingP/(J_LII'III'IIII.x'iI— III'III'I’IIL' DunitesDHIIII‘IN were\xCI'C seenxCCn only«mix inin theInc central,L‘cnIi'III higher,IIiuIICI'. partsiIIII‘IS ofIII' Kamuthengi.KIIIIIIIIIICI I They'I‘I‘Cx are'L’IIC xIInIIIIIsimilar to:0 theIIL‘ melanocraticmCIIInL‘IL‘I‘u‘iiC portionsIIIII‘IuIiIx' of01' theInc BelhelvieBL: L'IxiL' troctolitesII'I'IL‘IIIIIIL‘x as{Ix describedLIIi'riIICII byI) SIC‘ALIIIStewart (III—III.(1946, p.3‘. —I"I‘ZI472) and inIn hand-specimenEIIIIILI—xI‘CCiIIICII areIII‘C LIIII‘Ix.dark, L‘LIz‘IIpIIL‘I.compact, waxy-looking\‘x'LI\_\'I\II)I\In§ rocks,‘Ixx. IIIthatII IIL‘IIweatherIIIICI‘ \IwithIII‘I LIa brownI‘I'II“In and pittedIIIIIL‘L'I .xLIi‘IIIL‘C.surface, IIICthe C‘L‘Icolour'ILII‘ I‘Cingbeing mainlymziinIx' dueJULY to10 iron- 1\ staining.inmg. TheyThcx L‘nnxixiconsist ofIII Iolivine,I I aIxmsmalliI amountIIII‘IIiIImI ofLII interstitial..I‘I'. C:xIIII.;IIplagioclasei;Ij.".I‘L'I;x“C andIm. an IICL‘LxxLI._-.accessory darkLIZIIIx' mineral,iIIIIiCI.I.I. probablypioIIIb picotite.piL‘LIIiIL‘. TheyTIICII :II'Care piIiCIItypified byII). iL-sczispecimen 45/102‘5 III: II—iu.(Fig. .‘III.3b). In thin sliceiL'L‘ itiI is1.x SCCIIseen thatIIILII theIIIC olivineIIIII. inc isix‘ inin fairlyI‘iIit'II largeIIII’ge gI'LIInxgrains thatIEILI'. haveIIIxL" .xIII‘CsufferediL’ILI littleI: IIIC serpentinization,xCiIILiIIII 2/: Hip I‘. butI‘LII LII'L‘are surroundedxIII‘I‘LILInLCLI byIn). two-zoneI'IxI.I-/.I.IIIC reaction1‘52: IEIIII rims..mx. TheIL‘IC innerInnCI‘ zoneIOIIC consists.‘Ixnxix‘Ix ofIII I:a colourlessLLIILIIII.I3.x'x mineralmII‘IL‘I‘iII withIIIIII aIII fibro-lamellar:IIII'L’I—IIIIIIL‘IIM habit,IIIIIIII. refractiveI‘CI‘I'IIL‘InC indexinLIc CIIIx‘L‘close IIIto thatII‘I‘III IIIof IIIIolivine,xinc I‘HULICI'LLICI)moderately high birefringence,i‘II‘I. InuCnL‘C. andIInII positiveposiIIIL‘ elongation,L‘IIIIILIIIEIIIII. thatIIILII isix‘ probablypI'IILILI’nIx anLII] orthopyroxene.LIIIIIII pxIIIxL iIL TheTh: outerL‘IIIEL‘I' andLiiiLI wider“ILICI rimIim consistsL‘oiixix‘Ix' IIIof a colourlessCII.'(‘LRII€.\\ LIII‘IDIHamphibolebI IC inin whichxxI. iL‘II greenL’ICCII xpinCIspinel isIx intergrowninILIgiIIxx'n usas an extremelyL‘I'II CInC’ix' fineIiIIC .xxIIIpICIiIC.symplektite. TheII‘IC IILIIC:outer rims‘inix IIIL‘are oftenIII‘IL‘I‘. narrowIIII Iioxx whereIIII‘IL‘I'C theIIIC olivineIIIiIIinL‘ crystalsL‘i‘xxI‘IIIx are211C closelyI;II.IxL-I_x' >IIIICCLI.spaced. ScatteredSCIIIICIL‘L‘. indiscriminatelyIIILIixCI‘IInInIIICIx throughII‘.:‘I:~II;II‘; theI'nC rockiIIL'Ix areIIIC small.xI.I.III .x'IiIsubhedralIIL’LIIIII grainsLIIIIIIIx' andIInLI octahedral‘ICIZIIICLII'd ofOI Iia partlydIIx opaqueIIPLIQLIL’ mineralIIIInLI‘III which transmitsIi'ainx'iiIII. lightIigIII inii‘. patches,IIIIIL‘IIC. ' whenIxI‘ICI‘. itiI is brown.h: mm. This isix‘ probablyiII‘I..IIIIiI‘IIx' picotiteIIILLILIIC LIIandILI wherexI IIL‘:C itII iIL'L‘I:Ixoccurs inii‘. IIICthe IImpII:amphiboleIJCIC LLII‘IIIIcoronas;ix itII isix rimmed:in. .IIL-‘LI byh} .1a brownIIIIIM zone.mnC, A% palepale bluish-greenIIIIIISII LIICCII. spinelmind isis alsoIiIx’LI presentiII‘CxCI‘. interstitially,inICIx‘IiIiIIiI}. inin relativelyI'CI;III\CI} largeILU‘gL‘ irregularii ,_I. lIiu} grainsgiuins and occasionallyounxionulfl. asax IIL‘IIIIICLImoctahedra associated:IxxIICILIICLI withxiII xIIILIIstout crystalsCi'xxl iIx ofIII a:I colourlessLL‘IILIiIiIcsx amphiboleIIIaIIaL‘ (tremolite(II‘CnIiIIIiI: ?)..II. TheTIIC AIUI‘I‘I‘IZI‘I‘IIL’Iamphibole rarelyIII: 5.1: IIIIxCISCtraverses theIEIC I'IIiiICxolivines IIxas longInn; narrowIIIII‘I‘L'I‘Ix allotriomorphicLiIIoIIiLInIIIIpI.IL crystals.LixxIIIJx. SometimesSumCiimcx itiI isix associatedIixSiILiIi ICLI with aA phlogopiticIII.II.25I.IIIIIiC mica.:niL‘II. ThereI'IICI’C isIx littleIiIIIC plagioclase-aboutIr‘ lK‘L‘ILI‘C’ *LlI‘I"'.iI fiveIixC perI‘IL‘I cent-interstitialUCI‘Q’ IIIIL‘i‘xIIIIIII toI0 the:I IC LIIixiiolivines;Cx: itII is:x optics.opticallyI} positiveIII;Ix:IIxC withxxi‘IIi ;Ia fairlyIliiiIx' highIIIL'II refractiveI‘CIIL“:IL‘II\ ‘ indexinLIC\ and isIx pI‘LIIprobablyIIblx labradorite.IIIIII‘IILIIII‘iIC. ItII isix consideredCIIIiiIL’i‘CLI thatIh‘IiI theIIIC coronasCIII‘I’II‘q roundiIIIind IIICthe iIIolivinesi\Ia .Iicare LIIIC‘due toIII reactionIC;ILIiLIn \IwithiIII theIIIC felsparIeIxI‘ui inin theIIIC presence[‘ICxei. 03 IIIof late-stageI'IIIC xi; -C. liquorsIiLIIIIJi'x (c.f.IL‘.!. Stewart,SIL\\IIII. Belhelvie,BCIIICIxiC. 1946,I‘HII. p.II. 472).473. CoronaI (III‘II‘II structures.x'IiIII.II.IiCx aroundIIIIIJIILI olivinesLIIixia '.II'Care well\It'II knownIxnmxn fromI‘mm numerous basicI‘LI\IC intrusivesInIi‘IISixcx throughoutIIIi‘LIIIgIILII.II theIIIC world-Belhelviexo‘iLI RCIIICII.IC (Stewart,I‘SICIq‘I. op.II/I. cit.). and:IIIII RisorRixm' IH'IIIL'II,(Hatch, Wells\VL‘Iix IInLIand Wells,\\ cIIx'. 1949,III—III. D.p. 286)IHIII mayma) beIIC LIIIIIIL-LIquoted as‘LH cxIImIIICx.examples. In bothI‘UIII casesxcx theIIIL‘ inneriniiL'r rimsI‘Imx are:II‘C composedL‘IImpIIx‘CLI iII‘of III‘IIIIIIIxI‘Incorthopyroxene, while\x IIIIC theInc outerULIICI' rimsI'Imx areIII‘C formedI‘III‘mL-LI ofIII IIa L‘LII'ITIITII‘ncumming- tonite-spinelILIIIiIC-xpincl symplektite.xitpcIIiIC. TheIIIC KamuthengiIxIIiiIiII IiCiIui coronasCIIIIIII'Iix' are'III‘C x‘imIIIII‘.similar. As\x IIIat Belhelvie,BCIIICI-Ifc. thereIIIL-t‘c are‘IH‘L’ dark brownbrim n .xpinC‘Ix.spinels inIn theIIIC rocks,iLICIxx. A varietyIII'iCIxx ofLII theIIIC plagioclase-bearingpiiiginCIIIxC~IiczIIing IIIInIICdunite isIx: representedI‘Cpr'CiL‘nICLI byII) x'IIL‘CimCiIspecimen 45/100,3..“ IIIII. which\xI‘IICII isix generally iIII.similarI’ toIII theIIIC SI‘IL’CII‘IICI‘.specimen IiCxI'I‘iI‘ICLIdescribed :I‘naboveIIIC butI‘IiI containsCLIIII;ii;i.x moreIIiIII‘C plagioclaseI‘ILIL'IOL‘IIHL‘ and II.a fewIL‘I.\ grains of III:::I:Caugite andLlI. LI hypersthene,IixpLIxIIiCI. 6. mmand mightmignII wellI.xL'II beIv: calledI"IIICLI gnbbm.gabbro. InI i hand-specimenIIIIIi‘III x; LLII. :n theIn: rock is generallyLICIIL’IIIEIx iniILI:similar toIII theIII: normalIIIIIII. I.I plagioclase{‘IL‘ILLJi.IILI IxC dunitesLI. II . .‘x’ butIILII whenxxIICn freshI:‘Cx:I hasIIIIx brown.IiIIIII. ii xp:spotsI inIn itiI whichxxI.. II :iILare LIIICdue IIIto IigC'L‘gaICx’aggregates ofLII' hyperstheneIpCix. cm and :III:.augiteIC betweenI-CIxILCiI the:IIC IIIixolivines.ia‘. Round IIICthe CraL‘kCLIcracked I.IIixiiIL-.\'olivines thereIIICI‘C areLIIL‘ LIII'IIItIIcorona s‘iiCIiii‘Cxstructures ofIII" III‘IIIIIIIxI‘IIICItL‘orthopyroxene LIIILIand ;iIiIIiI‘IIIILamphibole-spinel‘- x'pinLCI x’xmsym- plektite.PIL‘I-{IIIE‘ InIII xLImCsome L'Iixe'xcases theIhe inner rim CIIiix:xIxconsists LIIof indiindividualizediL'IIi'IIIi/Cd LIi'IIiizxgrains IIIofIIIghIlight purplish-puiplixh» brownIIIIIIxn pleochroic{ICI IL I'IIIIL‘ hypersthene.I‘pCi'xII‘IITI'iC. Grains(Janinx and'IInLI crystalsCI‘xxIIIIx ofLII picotiteIIICLIIIIC areL‘IIC scatteredxLIIIIccI sporadicallyx932: L;iI]x throughIhi mush theIFIC rock.fi'ILIx. . A secondSLLIInLI >i\oniIiCsaxonitic varietyx iiiCIx ofIxi theIIILIplagioclase-bearingIILIIIICI IxC IIC II in. ‘LIIdunitesiniICx isix representedi‘Cni‘CxL‘nICLI bybx xpCL'iInCiispecimen 45/109,I15 I09 which\IIIICII CiIIIx:consistsx1> mainlyIIILIIIIIx ofIII olivine9l inc and hypersthene.tPLIIxI'na'. TheFIILII‘IIII‘IE}faintly pleochroicIIICJCI'II'IIiL‘ hyperstheneIixpCI‘xIIIL‘nC occurs iniII largeIII: gC SiiiiICJstriated Lcrystals.xI.I..x with\‘\:II1 ironiIIIiI III'Core inclusionsiIIL‘IIIxIIInx .III'IIII.Ialong theIIIC L‘Icmx'Iin.cleavages, LIEIII‘IIIgamong fairlyI‘zi' coarseI.‘r.‘2II‘>€ allotriomorphicallL‘IIi.oinLIIp.IIL grainsgIIIrIix ofIII' olivineI'IIExInC whichxI IIICII areiIt‘C serpentinizedxCI‘IIcrtziIIE7CL‘. alongLLIL‘lIg cracks.Cj‘I‘IL‘Kx. The'l’EIC olivine is a:1 magnesia-richIII:II.IIIL‘x'E'I-I‘ECI‘I variety.‘IIzi'Ic TIICI‘CThere IIareII‘C inIn IIIILIiImnaddition x'm‘IIIIsmall :IIIIIJIII‘II‘x’amounts ofIII“ interstitialinIL‘I'iIEJI pargasiticpm ‘lLISIIIC amphiboleumpI‘i Inn]: thatIII II isix faintlyI‘IiinIIx pleochroicDICIILIIIIIIC in green,man. II:andIII xC'IiIICI'IL'scatteredI gi’uziix‘grains III»of :inan opaqueII‘qIC oreIII‘C mineral..IiiICi';II. A\ hyperstheniteIIHL‘I ix'IIeniIL (—15(45/105)III:I isix Iaxx’iIL‘iaICLIassociated with’IxIIII theIIIC plagioclase-bearing[ViLtgiUL’ILlSC'I'ICZII'IIIfl LILIniICdunite atIII theII'iL‘ toptop. of KamuthengiIxamIiIIIICIIL.i hill.:IIII. TheIIIC rock[OLIx consistsLunxixIx largelyI‘Lli‘gt'I_I ofLII different-sizedLIiI . IiI-xE/CLI grainsgniinx ofIII pleochroichypers-iILeLIChz‘IIic ‘nxpcrx- thene,IIIenC. heavilyIICLIIi\||._\' dustedLILIx'ICLI withx I'II ironII‘IJII oreIII'C alongiIILIng theIIIC cleavages.CICLIxLILtC'x. InterstitiallylnICI‘xIEIiIIIIx inin partspui‘tx thereIIIeI‘C isix. aII lightligIII greeniIICL‘II slightlyxIIunIII_x' pleochroicpICIICIIIIIIC CIIIIII'IICchlorite CnL‘IijIx'ingenclosing x'maIIsmall prismsIpI'ix'mx III'of ;Ia CIIII.IIII‘ICxxcolourless IIIIIpIIiII-IIIC.amphibole, which\iiC‘I however,hixxL \t’t. inin someSome placespI:II;C.x‘ hasIILIx‘ grownLII‘LIxII‘. intoInIIx largeI.II':.IC prismspt'ix’mx andIItiIII occasionallyI.ILC;Ii.Ii'I:IIIx formsfont-Ix :iggi'egI'iICx“.aggregates. (iICCIIGreen hornblendeIII’II‘IIIIICIILIC LIIxIIIalso LIL'LIiixoccurs massive,mIIxxnc. interstitially,iIII‘ILIi'x'IIIIIIII}. IItIIand III'iCnoften penetratespcliL‘II lIIL’x betweenhcixxecn Crxcrystalsx'IIIIx: III‘of hypersthene.II} IICI‘SII‘ICi‘IC. (iii)(iii Anorthosites.-TheseIIIIIIIIIIIIII'II I ~ TIICx'C occurIICCIII‘ asIix infrequentIE‘IIIL“I.IL.L‘I‘II'I bandsIIIIIIC‘x iniI theIEIC dunite.diiiIC. SnSpecimeniIIL‘II 45/107,45 . whichxxIIiL n in hand-specimenImnII--xpLC-im n isix white\IhiIC iIhwith IIa blue‘.III.iC tinge,IIIILIC isIx‘ IxIIitypical:II and mademadc upU?‘ 02of labradoriteIIIIIIIILIIIIIIC crystalsI_I\‘~I£‘..I~ \Iiof varying‘IL'II_\I sizes,xILL‘x. withI.I II xIIsmallI.III :IIIiI.amountsII Ix ofIII chloriteC II IIIIC LII‘I.Iand xL‘IIIIscapoliteIII!C;1II.IIand xInIIIIsmall flakesIII‘IILL‘x LIIof muscovite..nixCIIIIIC SpecimenSINCLIIIICII -45/110‘I'iI'I isix composedCIIIJII IxCIi ofIII” aII pale-blueIIIIC-IIILIL‘ labradoriteI IIIIIIILILI: iIC with\I.:i Ii sharplyxilfi'mi IICIIIICLIdefined sub-circularxIIII—L‘I'L‘III: " spotsx'pm‘x‘ ofIIII'IIIII‘IIIIIL-ITILII‘.hornblende, whilexxIIIIL- scattered throughi‘ I‘iILIIgII theIIIC rockI’I CR .zI‘Care .Ia few‘L‘ I. crystalsL; I_x‘i.iIx ofIII. biotite.I‘ILIIiIL“ andiinfi. chlorite.CEII IziIL. TheI’IiC hornblendeIIIII'IIIIICII..I.: xIIIIZx'spots xIInILIsometimesI.T‘.L.\ coalesce.i‘IziLx‘L‘L‘ into:I‘IIJI bands:‘IIIIIIS andLII‘IL.‘ lensesILI‘xL‘x I‘Ixjas isix seenL‘L'II in specimenx; cciIIIeI‘ 45/112,if I If. ini:I whichIIIIIII’” I. the{III} felsparIL‘ixI‘I‘III' isix bytowniteEIxIII‘III IIIIC andAnd thein: darkII "Ix bands‘I‘IIIIIIIx‘ are:zIC composedCI. InIUxCLI eitherCIIIICT ofIII'III'II'IIIIICIIIIChornblende and'IIIII.I I_I'.;I‘dark green spinel‘ III‘IIIIiiII'IIIIILnLIL‘.IIIIor of hornblende alone. The1 ‘III‘ZI'I'L'.spinel is‘.~ probablyI‘ .'II.‘.:I“'.j. pleonaste.iIICI 'i.ix.L'. 14 These rocks may have arisen by the segregation ot‘of l‘elsparsfelspars during crystallization ol'of the dunites.dunites, with subsequent intrusion as anortht'isites,anorthosites, in which [liethe compact amphibole- spinel lenses may represent segregationssegregations or inclusions. The l‘oliationfoliation may have been im—im- parted to the rocks during their formation and emplacement in their present position' {is-'1(iv) Actinolite-Anthophyllite.ztr-n'imti'rr’wtmtmpi'it'i’i'i'i'c Rocks;Rocks.-InIn the eastern part ol‘tbeofthe hill actinolite occurs with anthophyllite in a IS-inch15—inch thick lens,lens. The antltophyllite.anthophyllite, which is fawnlaw-n coloured and has a silky lustre.lustre, occttrsoccurs in long straiglttstraight tibresfibres which i‘ormform columnar aggregates with prominent cross—fracturescross-fractures Hi(45/115).I lit. In the central part ol'of the tenslens the fibrousiibrous agg-‘cgatcsaggregatesr ol‘of hard brittle anthophyllite tip.up to twelyetwelve inches in length are transverse to its length. .-\tAt the margin the columnar aggregate gi\giveses way to a two to three inches wwideidc lcltfelt oi‘of green pleochroicpleochrofc actinolite needles and prisms interspersed irregularly among short crystals ot'of antltophyllite.anthophyllite, as seer.seen in specimen 4545/116.[16. In some marginal parts ol.of the lens there is little anthophyllite and the , acactinolite' olite forms a I‘oliatedfoliated mass 01'of larger anhedtalanhedral to eubedraleuhedral crystals.crystals, as seen in specimen 4.“-45/117.I IT. The lens lies horizontally along the strike lengthlcngtit ol‘of about thefive yards.yards, beyond which it grades laterally into a band olof actiuoliteactinolite and then into serpentine and magnesitc.magnesite. ’I'hescThese progressheprogressive changes agree closely with Hitchen's obseryationsobservations at KittyikiKinyiki hill tParkinsrnt.(Parkinson, 1947,194?. p. 33),.131. where cross—Iihrecross-fibre winsveins are composed of anthophyllite and alter at stirl'acesurface to magnesite. By analogy some ot'of the many anastomt’isinganastomosing mag:magnesite' e winsveins at KamuthengiIxamutbengi may be replacements ofot" asbestos veins,teins. thoughthottglt no e\idcnceevidence was seen to indicate that such is the case. The country—rockcountry-rock surrounding the dttttitedunite at Kinyiki is hornblendel‘:orublent'.c gncissgneiss and HitchenIlitcheu concluded that the asbestos wwasas t'ormedformed by the metamorphism ol'of raftsralts olof the gncissgneiss in the intrusion. The country—rockcountry-rock is mainly biotitcbiotite gneiss arottndaround KanttithcngiKamuthengi so tarfar as can be seen.seen, and there is no evidencemidencc whether or not the asbestos was derncdderived t'rontfrom horn-horn— blende.hlendc. (v)[\] Serpentine,S't'rpr'nrr'rit' andanti" MagnesiteUttgttrs‘irt RocksRoots occur in apparently \'vertical‘tical lenses with a thickness ofol' about tentest ft.[t which run north-southnorth—south and.and, being more resistant to weathering than the surrounding rocks,rocks. they stand uptip as low ribs that are presumably in wire.situ. The ribs are com-com— posed mainly ofot' brown-red serpentine which weathers with a dark brrwyn.brown, irregular.irregular, earthy»earthy- looking sttrl‘acesurface and is honey-combedhoneycombed with \at'iablyvariably narrow ramifyingrainii'ying \einsveins oz"of bone magsmag- nesite. Set in the serpentinous mass there are crystals ofoi a green inicaccousmicaceous mineral. Thethe serpentine is represented by'specimcnbY'specimen 4545/108,HIS. the bulk ol'of which consists ol‘of a massive brown alteration product showing weak plcochroismpleochroism and moderate birefringence that isl.\ probably iddingsite. It is finelytiuely veined\eined by chlorite and on a larger scale by magnesitemagnesitc which in part is margined by chalcedonic silica.silica, and encloses crystals ol~of a positivepositoe colourless amphiboleamphibnle and more rarely antigoritcantigorite crystals. A few pools ot'of chlorite are also present. (fhloriteChlorite t—IS(45/46)4b] was also foundl‘ound in the soitsoil as large green flexibletlcsible subhedral plates measuring upup. to sissix inches across. Its optical properties suggest that it is penninite. 'I‘hcThe magncsitcmagnesite winsveins are mainly narrow.narrow, \aryingvarying I‘rontfrom microscopical \enlctsveinlets up to \einsveins half an inch wide. In parts otof the hill pieces were Ioundfound that must have come from \einsveins. three inches wide.wide, but no such veins\EIIIH were sec:seen in situ.vim. t_\it(vi) PegmatitesPt’3’rllitftlt‘t‘a' um!and QmQuartz"“ term;Veins.-InIn the western part ol‘of KamathengiKamuthengi hill.hill, and dc—de- ntztrcatedmarcated from the ttEtra—basicultra-basic rocks by the edge ol‘of the thick scrub.scrub, there is an area ol‘of graphic pegmatitepegrnatite consisting ol'of coarselycoarsely- intergrownintergro\\.'n uttart7quartz and nticroeline.microcline. The pegmatitepcgmatite e\tendsextends froml‘rom the edge ol'of the scrub to the base ol'of the hill wwherehere the surl‘acesurface suddenly becomes undula-undula~ ting and slopes gently away to the nearest \ytllt‘t"t.':tlll‘.\"..‘.water-course. Although.-'\Ithough lloatfloat material l’romfrom it occurs in this undulating country.country, there is no eyidenceevidence fori‘or intendingextending ttthec boundary ol'of the ultra-basicultra—basic complex beyond the base ofor" the hill. The central part ol'of the pegntatitcpegmatite mass is mainly composed oliof m'isshcmassive cloudy quartz.quartz, though small grains oiof clear quartz,quartz and smil!small scattered flflakesakes ot‘of mascmitemuscovite were seen. Lying in the soil at the base of the hilthill below-below the pegmatitc.pegmatite, there are scattered flakesllakes ot'of \ermiculitevermiculite which may be deriyedderived t‘romfrom the pegntatitepegmatite or may possibly be contact alteration products ol‘of the biotite ot'of the gneissic country—rock.country-rock, tlcxelopeddeveloped in a manner similar to the vermiculite I'oundfound at Kinyiki t_Parkinson.(Parkinson, 1947,liJ—li. p.1.. 35-].35). In several parts ol‘of the hill.hill, massive titrart/quartz fragmentsI'ragincnts were seen which presumably come from quartz tents.veins, but tltetrtheir relation to the masstyemassive graphic pegmatite could not be determined. {\(vii)iit Plagioclase-amphibolitesPi‘rrer‘rJt'i’nsc—wnpi’i,r'i'icu'r'rr’s occur as senotithsxenoliths in the dunitcsdunites and l‘orntform a \at‘iablevariable but distinctixedistinctive group 01'of rocks in the field. One type is represented by specimen :545/103,103. which is a blue—blackblue-black tine—grainedfine-grained rock.rock, speckled by small t‘elsparfelspar crystals and weathering with a thin dark brown crust. It consists ot‘abozitof about three parts green hornblende and about one part ~ ~ ~ ~ 15 andesine-labradorite plagioclase, with small grains of magnetite scattered throughout. The hornblende and felspar form an even-grained mosaic, the felspar being interstitial or en- closed in the amphibole. Clinozoisite occurs sporadically in some of the felspars, some of which are completely replaced by a pale brown isotropic material studded with clinozoisite grains. A second variety is represented by specimen 45/41 which has a melanocratic portion sharply demarcated from a portion that has less than 50 per cent hornblende. Specimen 45/41B, which includes the junction between the plagioclase amphibolite and the dunite shows gradational variation from more le:.Jcocratic to more melanocratic p::>rtions. The dunite appears to be altered and mixed with the plagioclase amphibolite but only at the contact. Specimen 45/48 illustrates another mode of occurrence of the amphibolite, in which there are patches and streaks of the dark minerals and sometimes hornblende porphyro- blasts, giving a mottled appearance. (b) The low hill south ofKamuthengi is composed of rocks similar to those on Kamuthengi. Topographically it is a narrow ridge 200 yards long and about 50 yards wide that rises steeply 50 ft. from the plain and is heavily bush covered, with few exposures. The hill appears to be composed mainly of plagioclase-bearing dunite (45/119) with a few masses of plagioclase-amphibolite, as well as scattered occurrences of serpentine and magnesite, represented by float blocks. The plagioclase-bearing dunite is seen in situ on the crest of the ridge. It has parting planes which run on a bearing of 110° and dip N. 70°. There is a small band of actinolite-anthophyllite rock (45/120) on the southern slopes of the ridge. The rock is green in the hand-specimen and has a silky lustre. It is mottled by small brown and fawn patches which contain anthophyllite fibres as weJl as actinolite, the brown colour being due to iron-staining of the anthophyllite. The actinolitic rock strikes on a bearing of 110° and dips N.N.E. at 20°, which suggests that the partings in the plagio- clase-bearing dunite are joint planes. (c) The ridge south-east of Twamagau is a low, gently-sloping ridge running on a bearing of 25°, which is also composed of ultra-basic rocks. The detailed structure of the intrusion is completely masked by the soil cover, but the trends of the intrusion and of the rocks appear to be the same as that of the ridge. The surface consists mainly of dark-coloured soil in which are numerous boulders of types similar to those of Kamuthengi. The rocks are mainly dunites and plagioclase-amphibolites with sparser serpentine, magnesite and chlorite and a blue-grey, waxy rock that is composed almost entirely of small interwoven crystals and fibres of anthophyllite (45/96). One of the serpentine rocks (45/54A) has a blue, waxy appearance in the hand-sp~cimen and weathers with a white surface with etched-out banding; resulting from the occurrence of parallel fibres of antigorite arranged along strings of magnetite grains and lenses at right- angles to them, giving a repeated comb-structure. Specimen 45/57 is a foliated green rock composed of flakes of chlorite obliquely cross- hatched by long bladed prisms of actinolite, pleJchroic from straw to blue-green, which measures in the hand-specimen up to three inches in length. Orif(in of the ultra-basic intrusions.- Thr; intrusions are essentially related dunite stocks that are unconnected at surface. ' They are intrusive into Arch L ,.-- 16 Ihe1'11L' intrusion11111'I.1\1LII11 ofL11' Kamuthengi1\.1.I111:111L"L1I__I" appears11111L'L11'x1L1to be11L so~11<:1111;11'1L‘1111_1~'L'1_11'1\::‘111"'1'11\.II"‘similar to those of Kipiponi (Kapuponi) in.1' v.1-L1'L11south Kitui}\ILL: L111Lfand Kinyiki1\-'. I31 that13111112111113:tentative L'L1I1L'11_1\1L111~'1L1111“.'111111111]conclusions in connexion with its.11gL':I.1'.L'}age and L'.origin. can'I be drawn"\11' from1.111111 them.1111311: TheT111: KinyikiK11111k1 intrusion111111.151L1z1 is1x post-metamorphism17\‘\-L'1I'1C1.L1Y‘.1L‘1"‘111\n1 1has is1 Ha}shownI1111'1 by1131 the131g presence1.’~L1L'L' ofL11'11L'~'1~'nests at:11 the111L' margin11:1111111 ofL11"largeLL11'IIL' L'L11'L121L111111corundum L'r'crystals"-\'TL11\ which11.111L1L‘. have11.1w not1101 been1‘L'L‘1'; broken,111'L'LKL'LI1. as. theyI1'LL"_\ 1111111L1would 31L1\L'have been11L'L"1'. had11L1LE 111:3.they been31L'L':'11pre-metamorphism.~1:1-L'1L -L1'1'311~1:1 T11L'The plagioclase-amphibolites111L1u111L'1'Ix"-'L11111I11111'-111L\' Lawcan 11:be reasonably1'IL'L1';\1111 111M mapped111.1:11‘L‘L1 L11at KamuthengikL11‘L'11111. M 1 and the'L‘1LI field11L'ILf relations'L‘IL'LL1L‘1‘.‘\ L111do not111'1 \'1;___IL'\L'.suggest that111L11 they111LI; :1";are ~1L'L':sheet intrusions' but111.1 rather".1IE1L'I' xenolithic\L11LI.111‘:L‘ inclusions.11"C1Lh10'1‘ Plagioclase-amphibolitesPILLIgiL' LLxc—IL11'L'LI11I111.L'.L\ a11.111L1'similar to1L1 the111'; Kamuthengi1\L111111'.: xenoliths...\.1LL;L\ but also L'.I:11L'-.IL:111'LIcontaining garnets1" CI\ and.-.1111\L'.111L1‘111L'11;1\L"-:.1L"c:1111L11'1'IL"LL111.1;11'\111ILLI;111LIL.1L"L1scapolite have been mapped near Mpwapwa in Tanganyika111121.111]- L1 Territory' by1.1L B.B N.I\_ Temperley1L'III'L1LL1 (1938).'1'131'41. T11L‘\L‘These rocks:'L1L'E-Lx areLLr'L' in1:1 x111-'IkL'I"L1L1L'~.1.1L'sill-like bodies, the centresLIL'1'1 ("1"1‘1"of which have ophitic structure, 1.1!."1LI1'Other 11111'L1-1'11HL'ultra-basic 11'111'11L1L'11xintrusions in11' }\L'.I1jL.1Kenya 1'..I\L'have 11L"L‘11been mapped1'1L111g1L1L'. Luas 1L12L'1'later :11in age than the metamorphismLI1L"1'L1111L1'1‘[11~111 of1.11'111L"the BasementBL1xL'1‘L1L‘:11 §3L\1L'111.System. That'1'11111 at111 Kinyiki,14111111. near11L'111' Mtito\111111 Andei,\.11LI.L'1 has already beenI“I‘L‘1 mentioned.L11L11111L'1g1cL1. 011131Other 01111111similar Li'L11"1L"dunite plugs1‘1I_1I_;~L1L'L'IL:1occur inII'L the111L' 101111south KituiK11Lz' L21~111L1;11district at Kipiponi,k111'1'LI111. Magongo\.‘.;1'__"LI11_L'LI andL11'.L1 KenziKL-WL I‘SLnL'1' At\1 Schzkuc.Selukwe, Mashaba\111a11111111 111‘IL1and Shabani31111111111 :11in $1111111L'1'11.Southern RhodesiaR11L111L'\.;-. (MacGregor,1‘.1'L'.L'(11'L'I_._IILI1'. 1947, p. 10) there. ' L11'L'are ultra-basic11111'L1-1'LHEL‘ 1:111'L1x1LI1'x'intrusions which\‘-1'1L,'1'1 L1'L'are L'1111s1L101L'Liconsidered 1L1to be11L'1‘1'pre-metamorphism in age. The rocks11.1k types11116 L11'L'are similar\:11'."1;1:' to1L1 those[:1L1x15'.11at Kamuthengi,'r\"L1111L.-:}1L':1Ic;l.1'L11but "in $111111Southern Rhodesia there are more ~L'I'11L'111111L‘.111L1g11L'x11L'.111111;1\'11L'~'1L1~1111L11L's'.serpentine, magnesite, and asbestos bodies. Also,\11L1.;1181:.111;1111111Cat Shabani the ~CI'11L'111111131'1;1'11'U'L'1LK1'1'LI"serpentine has been silicified and: L11 In111 north-western11111'12‘1—11L'xic1:1 SL'LIH‘LLHL‘.Scotland there1"1L'ILI'L' ILLI'Lare many111.1111} small~111‘L11] 1111";1-1111~:L'ultra-basic 1111L VI-METAMORPHISM\ l—MI'I'I \.\I()RI’HI.‘~1\I The'111L' 11.11%bulk 11"of '.11LIthe rocksE'I‘L"\\ L13'of 11cthe LareaLIL';-. represent an originally_ sedimentary series.L' that has1x been'IL:C'I~L1"1_L'CL':CL11L1111IL'II1xL'3111'L'\~.11':.'11subjected to intense pressure, heatI. and'. ._.".granitization.'. The.. metamorphosed.L L ' IIL1~LIL1 sedimentsI\ .11'L'are Lwi'tL'71often banded,1.1:111L‘1L31i. partly1 1111) 1.1111;due toII.1 the'LLIL' preservation\CI‘LLLUUH 1‘1of original interbanding of 111'”:argillaceous'l'_IL'1L 2111‘ and L11'L'1121L'L'LI11.~arenaceous L'L11'111'IL'11L'componentsL111~ L111L‘.and partly to111 preferentialI‘IL'1'L‘L' {'11 granitization along certain.1 planes,11:11..» giving quartzo-felspathicL/ILI-L'L'1s1‘L11111L' bands..“IL1I'II.1\. As sillimanite has developed in pelitic beds itLL '1is \"_"'1L“L"obvious that the metamorphism:11L1L1111L1:;‘I11~1'.I was1'.-1‘ L_LI.of LILa high grade, corresponding with the sillimanite zone of ~.- 17 Barrow191.1:1'1‘11 (1912,11-112. p.p. 274).:41. TheTi1e1e111;‘e:temperature11 1': was1.1m probably'1 11111111} high1 enough to causeL‘.\1.,‘ recrystallization1'1L'C1'gm1111'1‘1 :1111'-i‘1 and.1111! 111to 11111111allow flowmm in111 the gneisses,guano. although. 1101:5111. 11mm"these phenomena1‘1'1e1111111e11e probably I‘Lfe'llloccurred‘1’1 11while:1111: the rocks;'.'1e'\'~‘1\e1'e'1111mh11111111.:were in a solid though plastic state..216. ()1:On the:he metamorphic:‘ne1111t1m1'1‘hie 1.1;‘;e~facies dLhmlTedlh‘Wclassification 1.»(e.g. Turner,.L."1'L"_ 1949,1 p.I. 76)"1 mos”71.)":t 1"of 11cthe rocks-1)LV’\.\ fall11H? into111111 the potash-sufficient11111;:.~f11->111he1e111 section«1:11.111 11:of the13‘1“ staurolite-kyanite'x'... .'1\'111e-‘1\“\;1:'111e ~11h-1'.1e1e~'sub-facies 111111:of the amphibolite.111111111h11h1e facies,111.111.; ‘.\11hwith the'. e 11we1‘ahkigeassemblage-- biotite-hornblende-plagioclase-microcline-q"we hie-1.11.1.1“uartz and when more calcareous- ~ diopside-hornblende-plagioclase-microcline-q1T1.11‘\11TC-T‘1.‘T "11“ _ :‘we‘..1"e-e11.;uartz. The[he sillimanite-almandine~11.1111111111e-11131111111E11'1 sub-facies\1.'..‘-- ‘111‘1Lx of11" the1h: amphibolite.11'1‘.;7-‘1‘.1\11111L‘ facies1115 \J\ is1x .2also~11 representedFCIN'CHC'TIL‘C by1“. the assemblage-:1» sillimani te-alrnandine-plagioclase-quartz-orthoclase.:1.1111‘. 11e—1‘111gwe‘..v.w—1;1_:1.1'.'-1.1'11we‘me All the gneisses now contain more felspar than1E1.1:1 is1\ found{11111111 in.11 most1111M \e.‘.1111e:11111'j.sedimentary rocks,reek» and it is considered'e11 that111111'111.e{11‘v!much of it1'. must:11.:\1 have1““ been introduced, probably by granitization,11.11111.1'.1‘.111"1_ but what11.11111 form11 1'11! this.'.\ processFONS“ took".1\11\ is\ doubtful.1‘11: From the even distribution of most111.1% of.“‘ the1P1; felspar, it is'\ judged1.11 413.1 that11“.;1 it1: was\\.1\ probably effected1‘eete1‘. by"j. .1..11e:quiet permeation,:1 thehe formation11.‘v":'1':111.1:1 111'of bands being duee to1.1 segregation«11115411111111 or111' preferential1‘:'e1'e1'u:111:1i permeation‘1'111e.1111‘11 along.1111 certain-':'1 planes.11111110. Evidence3 \11‘.e1'1ee for quiet introduction.1111111111.11e1'1111of material is[\1‘111111111111311‘\11'.11111'.,r.11111:1«newfound in the granitization series- (a)...‘1hn111‘g:e.11.-11~‘1"11111.‘1_;:‘.e'\~:homogeneous biotite gneiss; (b)15111 porphyroblastic1‘1‘1'113‘1}1'11'11111x11e gneiss;5111b“: (c)(111111;:1-1114111‘1“:augen gneiss; (d)11.111 bandedhuhdee1 gneiss;31w: \x. thethe111embe1<115'\\.hieh1'e111'exe11tx1.1g;exmembers of which represent stages 111'111e1'e11~1n§;of increasing intensity1me11~11§ n,"of granitization.1111, The permeation1T-e1'111e1'11m1t may1:111} havehme beenhe”‘11 byh} aqueous111111C1111~ liquors{11.111111'x111'or byh_\ ionic111111C1111T11x1111111111111diffusion through the solid rock,ruck. reaction:‘eue1i1111 with11. 11h the1111" hosthwl minerals1111;11:1etx leadingfinding to111 the1h»: formation11111111111111 of1'11‘ alkali111M111 felspars."133111114. During”11111. the111C process1‘I'1‘CC\\ recrystal-:‘eer'j\\l.1‘— lization10.113111 in15‘: some\OH‘N caseseasex removed:‘enmxed the1he effectsCHL‘QH of111' earlierc.:1‘11e:' shearing~31e.1:'11 stresswe“ imposing1111;7cn11"; granitoid,g1'.1111:1~.1‘. textures1e\=.'.11'es onm1 the1he rocks.mekx. Granitization(11'1111111/1111111‘. did11:11 not2111'. effecte1Tee1 the1he calcareouse.1‘1e.1:'e111;~ rocksweb exceptea ‘ep‘. marginallyn1.1"gi1“:11|} and111111 along1111111;1 impure11111‘111'1‘ bands,111111115. probably111113311111} becausebecame on1111 the1111‘ whole\1 hule they1he_\ remained1'e1111111'1e1i compact,e111111‘11u1. which'11 hueh suggests~'.1*":-_IL"\1~ that111.11 granitizationr» '1111'111/11'121'11‘ wasmu mare:11'11'1" probably1‘1‘11111111’). the1he 111‘11111‘action 1'1of liquors11.3.111w rather1.11.316? than'.h.11'1 «1"of xvii-1!solid diffusion.unuxiun. VII-STRUCTURESVII H'I'Rl ( 'I'l Rlih The area hashm in1:1 parts11.11% eenucomplexflm structuresx11'12e119'124 11.1:due 11.1to 1111'the \1:_1‘e'superimposition1 1'31 1‘.1\11.1~1' 111of minor12111201 folds1.111135 and.11111 e111111‘1'1111mcontortions 1111on theLhe major11111111 folds.101$. Thehe 1511Mdips of111' foliation1111111111111. are111': high,h‘ Y T1 averaging'.1\e1;1g11‘1g uhuutabout NT60°, and111113 strikesslz'ikex are111': in11‘. generalgem-C1111 essentiallye>~e11111:1[_\ conformablee11111'111'11111111e 111thwith the1he regionalregm‘. roughlymugl‘i} north-south"1m'1h-x'11111h «We.strike. Faults.-In{1111/11. [:1 the1f1e south-west\ULllh-HCH there113e1'e is.~ a11 fairly1111?}; regular:‘eg11111r' north-south111wr'1h-x11111h ~11'11-.e1\111‘..:strike with a prevalent1‘1'e\.1Je111 easterlye;1~ic1'l_\ dip1hr whichwhleh changesch.11'1"e\ abruptly4111111111) in the1hc north11.11'1h to111 a11 north-east-south-west111‘1'131-1_".1\1-s11L11]1A\\1_‘<1 \tt'ilxestrike with111111 north-westerly1‘01}? -.\c<1'e:"1~-. dip111:“ (Fig.1113?. 4).$11 BecauseBequme of111' this1h1~ abrupt.1"111‘1 change1'1‘111‘ ' it11 isxx considered1'111tx111e1'e1‘1 that1.11111 there1he1'e is'.\ -..- | . .1 21- I,“ ., 1 .'. '_ . .. probably1 1‘1.\. l\ a1: faultIL .111 between‘11L.\\1_L1 the(he two1111‘ blocks101111..\\1_1‘1of country1.111111.» with\x11T differing strikes. No\11 fault111.111 wasmm seen~-.‘e:'1 on11:1 the1he ground14:111. 11.1 but11111 a.1 line1:11e hashm been insertedhive-111‘; on111': methe map11111;“ just_.'1.\1 north1‘: . of Tia and.11111 Myethani\1_\e1“1‘ 1 asLb the1he most1111M probable1‘1‘111mhle site~11: of111' a.1 fracture.11'111'1111'e. The rockswe)“ on1111 the‘1".1.‘ highh1gh ground2111111111 betweenh ve=11 UumaaL 111111111 andend. Endui111-3 and11111.1 betweenhe'V-een Kyui}\_\111111111\\e11and Wemanzi'«1 have:1. e1111111\\'111__'opposing dips,1.11x.\which1eh ~11gee~zxsuggests the11m presence:‘ex‘cn 1‘1'of a. broadhunui syncline\‘_\11e1‘1‘.e or111' fault.1111111. BecauseRemuxe of111 the2“" sudden change'.1“.ge 111;.111111111of attitude 1‘11‘111eof the rocks1'1‘e1u betweenhemeen Endui,}'11d1:1. where they‘ ' are'e well-banded\‘1e11vhz111.1e1‘. and.11‘111 regular:'e_ with1 a:1 north-south1‘1 1;"1—~.~.111‘1 strike6.111.." and11111". WamwathiH 1;111\\;1‘-.h- where'C1‘e the111C rocks‘m‘kx are.11; more111111": closelyulnar.) folded:‘11h1e11h11hwith north-east-south-west1e11x‘. M‘UIT - strike, it' appears1 likely' that1:1:11 the{he structure~11“11e111:‘e1~_is, inE111'111:1_11T1111h.fact, a fault. Itl1v.1111‘:'111‘11hhwill probably run"'.11;'.1E111:;_1"1along the eastern footSnot 11.of theIhe ridgesringee betweenhemeeh Uumaa1".111'1 and Endui,'i1t111. which form11.11.11 a1= remarkably1911111'k.1"3_\ straight and sharp'11 feature..e‘.‘.1.151'e_ The nature and3111.3 throw of the postulated fault are unknown though.it must have' a throw of.1- less' than 1,500 ft., as can be deduced from the relation of the peneplains on either side of it. 18 Along the Mwanya valley, south of Ngeani, the Endui ridge and the Mutuangombe- Endui fault have been displaced by a tranverse fault-zone in which there is a series of minor faults. 0 30 S '" 0 0 " ~ . (;,"0900 '" -+ \ '-«--"" -~~"'\ ?, \ " \ '"'" - ...... l' '\ \ \ "-- ~i:-\ - "- - x, '" ....- ~ "- <,- ~ ~ --... l' "- '" "-\-- ~ ~1\ ~ , \ ...... D;p of foloo,;on -t- An,oc/.nol..i, P.ch and dorec',on 01 linea"on -+-- Synclinal~xis - -- Foult< ~ I,ocl,nol fold Scale 0 10 15 M,I., j J Fig. 4.-Structures in the Mwingi area. Dip faults are common in all parts of the area and run north-west to south-east with dextral displacement, i,e, the blocks of country north of the faults have moved south- eastwards. One exception to this is in the Mumoni hills where the northern block has moved westwards. A conjectural fault north of Nzui has been inserted on the map because of the sudden reversal of dip along the strike. No evidence was found to indicate the nature of the faults or their throws or displacements. Folds.-South-west of Kiormo there is an anticline with a north-north-west trend. West of Endui converging bands and opposed dips outline a northward-pitching syncline. After converging closely near Katui the marker bands continue parallel, with an easterly dip which ...... , iiiii 1 19 is considered to mark overturning of the easterly limb, forming an isoclinal fold. Lack of symmetry in the beds on either side of the axis may be due to lensing out of the bands across the axis of the fold or to a strike fault in the axial region. From comparison with this fold and the general steepness of the dips, with some reversals, it appears probable that the area is composed of many successive isoclinal folds (c.f. Shackleton, 1946, pp. 26-27). The rocks of the Kyui-Wemanzi ridge dip generally west, but east of Kyui there is a tight south- ward-pitching syncline. It is well displayed by the convergence of hard ridges and is im- mediately succeeded\w. L. my. westwards by an anticline. The axis of a large syncline lies just outside the western boundary of the area, and probably passes through Mumoni as shown on Fig. 4. The western flank of the fold has been demonstrated by Bear (1952, Fig. I, p. 5). J ‘ ‘v ‘ v v Several other folds“~ \ were‘ g x detected, V in the‘x area,K V but oftenk theyx arek only of short‘ deter-L‘ , minable strike length.: ‘ Theyih haveH . dominant\‘M‘ m ‘ roughlyw: ‘. north-south”m": M" trends:mnmand pitch,w mnorth“M"at low angles.1 \ Lineation‘ was“\ observedMw‘ sd‘in the‘ western portionf “ of theM area‘ and,w with‘ ‘ one,.exception," had' a pitchnig? of:H about(“:H 25°:3: along‘H‘w' bearingsi‘L‘w'xwwof 200.:“ It11 wasmix foundNW“ in‘ banded‘ ‘ ' L‘ contortedJ: ‘ biotite-, gneisses, k «'with‘ linearmm segregationx: ,171‘ of‘ the1‘ \ dark,» minerals‘ K_ x on theL‘foliation‘ planes.u ‘3 TheI; exception1‘ is» nearW Kiormo.\ in the‘x‘K‘Lsouth-westmy corner. ofw theWm“area, where\‘ the‘ lineation‘k, w pitches‘, k m at 250 to‘ the south-east. VIII-ECONOMICMa} EiH‘M'Mt'u GEOLOGY“Hymns 1.! BasementiiiII‘HH System\u‘h'm The{ Basement‘m‘ \V‘NKMSystem rocksk: \ in them¥ area\. yieldedJ no KevidenceL ‘u xof theL presencei x J A of economicallyl valuable, minerals.‘ \Neither graphiteu n nor kyanite‘ were found,v and“ the peg-n- , y , ‘ ' ‘ >1 M 1‘ : ‘ ‘ . 1, m.‘ 7,1, . matites\V proved, to be.p little‘ ‘ mineralized,“kw \ containing. “ L in“addition to‘ quartz.‘ and felsparW ‘ only‘ sparseu crystals\l V ofV biotite,V“ 7 muscovite“n7“ :7 and‘1 ‘Vtitaniferous7 magnetite.“‘ Brief‘J‘ 7 notes‘v 7 areJ 7 given7‘ 7 below“ ‘v‘ on4‘ minerals found in the area. (I) Garnet and sillimanite were;., found,vu » but‘ ‘m‘m‘Jknowhere in sufficient» K ‘, quantity,u‘IM‘v v to warrant_,‘‘ ‘ working. Search among the Mumoni“I hills1 may1 H revealM :1 bandsu \wof sillimanite-richx m' hi'u rock,‘ 1 but‘Hit is doubtful if they would be workable.in, W‘ LocalI concentrations\\‘\~'KH{[LV‘1V“JV‘\ of~ alluvial41““‘u1‘garnets\ mayW: also\H be found in the same region. (2) In the limestone bands there‘L‘w‘is oftenflhla large.1.: proportion of fairly pure marble, which appears, however, to have a variable“4 magnesia‘ ‘74") ‘ content.“H The marble could be easily quarried and calcined to produce lime but there‘1k:»x‘\17“‘»dis n::>local demand and lime can be more profitably produced elsewhere nearer to railways“Rx“and towns.‘ ‘* (3) Common minerals are more important in the area. E. Powell has worked ochre for pigment from a river basin infilled by Pleistocene ochreous clays south-west of Nziu. The ochre is limonitic (yellow ochre) but, on calcining, red and pJrple ochre and umber can be produced from it. Green pigments were obtained by using the green gypsiferous clays associated?.L'~\\\Lid'x('d with\\[- the ochre. In 1945, the only year for which figures are available, the pro- duction014.37“? of pigments was 11-tons, valued at £375. Gypsum is disseminated through the clay and also irregularly distributed in thin veins about half an inch wide, which sometimes swell to several inches in thickness or even into lenses a few feet thick, but it would not be economical to work. Pulfrey (unpublished report, 1946) found similar deposits south-west of Mutuangombe, and many more of the shallow valley basins with black soils probably contain gypsum and ochre. 2. Ultra-basic Intrusions Economic minerals are commonly found in ultra-basic intrusions similar to those of Kam'lthengi, and include magnesite, asbestos, corundum, vermiculite,‘\w.‘" chromite, talc, serpentine, mica and in some cases nickel, copper""3. and3m“ the[Ha‘ platinum:“Ummn‘ minerals. The dunite of Kamuthengi and the neighbouring intrusions"l I"? apparently‘1‘;"“'L;1_1\ does(‘1 ; ~y1~‘not contain these minerals in sufficient quantities to be commercially interesting.1". ;:*n,-\L‘:‘__'. FurtherIvan: prospectingmy by pitting and trenching might, howeve.r, revealL“\..’.i.-L“1”.L‘I‘...‘.economic quantities.1L3;:l“"¥Lir‘wu“of magnesiteI“ “3:: L-‘ \ or asbestos. L - roo 20 (1) Magnesite veins the dunites but as estimated from surface exposures the amount available is small and 'not sufficient to warrant working. Associated with the magnesite there are segregations:cgutmm ofUV- an earthy valueless serpentine. {:3(2) A\ horizontalhum/"mmv .' V lensI-"‘~ ofW ‘ anthophylliteLLV‘Mw'N‘L-“ J asbestosLM‘H‘ \sw. \‘VL-Awas foundM211“' in the eastern part of Kamu- thengi,V but isA onlyL‘Wifx (“UNIabout fifteenY‘RIICL" inchesHM; in thicknessiNk'xfl” 1m mu]and five yards in strike length. No indication»lL'L’.['U" ofU} otherJH‘C‘" asbestosJ‘!‘L‘\".L‘\ veins\Lfil‘w was\.L1\ seen.\L‘L’W 3. ‘iupcrficiulSuperficial Depositslh‘pusils (1)‘.5\\White“HQ sand suitablesmNu for"m concrete manufacture is found in the dry river-beds, notably those:Imxc n3of Micthe {mumrivers Wyn}.Tyaa, KatzeRM and Nziu. Local demand is small. ‘1'»(2) Road-metalKMuJ-vm1 inH: theH1: formmm: m‘of lateriticMuifiuc earthsL‘LH'H"\ is.\ monlyflj. found"lam 1 in1“ \‘THIHsmall isolated:MV‘J‘IL‘Li :k‘l'\=;\lenses ”21‘and bandshawk Lmdand um‘scqwfwyconsequently\ ixis mm»little used.mm, \Cw‘mNearby» dummmnnufdecomposed mpkrock and Kimfine-grainedgliiilicd punchgravels thatfirst Helie m'son them (1R3are mostmm: commonlymm ‘fw (a usedmun: form: road1. 3,11 knxgmaking. (3)F‘s No satisfactorymmiligzm‘v building stone“ occurs in‘ theElm areau and buildings are made from im- ported[N's' concretecnmrclu blocksNngb Mor from locally1&1:t kiln-burntn, "JV'WI a":and sun-dried bricks. Valley soils are commonlygummnnh usedlui for7b! them» manufactureInui‘LAlLulmt ofu. themy bricks.mm‘kx, At Katze,Rat/LL by11} theMic KamuwongoKmnuuoL bore- hole,'rmlc: umiand where“hero 1cthe Nairobi-Garissa\gm'ulwcumxm roadmad CH‘\\Q\crosses LE1:the riveru KangingaKmugmga nearmm\1\\H‘};Imc1cgMwingi there are brick-pits.i“iL‘3x~DiI\. The brickshi‘l‘c‘w areu sun-dried forTh" onemic day,d then‘11 builtNH}: intoH" ‘1 L1a clamp91 which is then fired for aboutUE‘HLS ten{cm Um)“days. TheI'll: resultantL. MW 113'1J~\;-“bricks are hard, even-grained' ‘21andg. gamma.compact. The pit at Katze is[\ {HEHH‘UHLH‘}continuously mullused myand fiproducesrmdmm .1‘about 12,000 bricks a month.I‘flxV'WH‘. 4. Alleged\lit'uud (Coal(ml DepositsDupmih La‘v n. . , 1' ‘ . x . «. -. ‘ - w. ! FromHu'n time1mm to’H timem.“ samples of bituminous‘ “L‘.‘L1..“\LJ\\ coaluni have‘JLl‘rR been‘L~ brought in from‘\‘!.1.-‘Lthe Mwingi\|\\ area.mud, DuringUm mg the coursean: of the surveyW‘j- auPHJ‘;ULLV:'httu‘n‘xi'1'11C'C\:'\k1prospector became interested inJ: specimens\pigmxm submitted\LIE‘Im to:n himmm byb} Africans\i'nmm ands. .I attempted tom discoverdiuu‘xcr' coalon] deposits.CCI‘uWHN A\ visit\m: wasm1 paidpan“ toIn localitiesimp nearnew: TwanagauT‘Aulmguu inm hishix companypmmpam and that[hut of01' an.m African\Ez'zmn guidegum: who\WM‘ \Inicdstated he hadhid found11mm the coal,gunk but[ml neitherHeilhu' coalam} normy indicationsmdmnmnx m"of itI were“(11* w;seen. (MOn ”clgeological‘ m! groundsgZ'L~LL:‘1d\ it1. is' most unlikelyLani kc!) that1'1111cwuicoal depositsdct‘mm wouldmmhf beW foundTh in the Mwingi area and itH is\ consideredu'mu‘, that the specimens recovered there are the remains of consignments of coalQUN taken£1w intoI'Mx‘v the area during the 1939-1945 war. 5. Water (1) SURFACE WATER TmThe I‘L'xx’amzuuw’procurement 0of “mm:water inH' the dry northern and mwc‘eastern part of9: the1h: Kambahamlu \L‘.Native ReserveRurmc prmcrpresentsflx L1a Smdifficult{gut‘\ problem.[‘mt“: , During)1H'Lw: Hm:the Himrains .md.and for. ‘ a few “wkweeks 4“afterwardsnumb llin V— The Local Native\Llll\t_”.,HL1NL’\1Council hasRh \N'constructed 233 MINsmall umi‘.earth dunx:dams at thcthe 1mmtime (‘2'of \u‘itmg.writing, with an'mcaverage'u capacitycupmmlx .s?‘of about m:two million gallons."x. Trouble[HULL‘WR‘ hasMix been1 caused(kulwu byt1} porosity] ‘\1!'\“H\ . w, ‘ of031w;the floorsI‘; 0l ofA“. INCthe reservoirs[C‘L'i w“ and by the bursting of'1“:the Junkdams @111during hum}heavy mx‘nrains hmmwbecause u;of inadequate.z'wduflmlr x]Wspillways.fl[\\;i}» TheTH: porosityg‘nj'nw' is gradually annulled hf.by I‘mthe settling of fine suspended mud111M intomu theU2: porespunk of" the soil on the floors of the reservoirs making-111cjnthem was?water-tight. (2) GROUND- WATER Ground-waterM-yuug: {\L'g‘Loccursfls ini? the“ areaw‘w min 1‘3:the Vlower part‘ ofm 1]:the zonexvi: 1)?of ‘V‘N‘AMCYLIL.weathering, the base21w .1‘of whichw ‘(m’mx'forms :man wunevencxcn surface rmgroughlyflb reflecting the:L‘ 1topography._ \\;:1w'Water TM.“flows dma.‘down this x'm‘z‘uucsurface and:md LLL'cmuLLELHL-waccumulates in its hollows and in valleys."_\~ The Africans\r'fimm Lmtap 'l‘mthe watermum i"in the valleys by digging pitsv up to 30 ft. deep in the dry ,',river-beds, ‘JHL‘and4 L_‘-1mby using yt‘.‘concrete-"'L‘IL" lined wells sunk by the Local Native Council alongside river-courses. Large resources"..I;L‘.\ {‘1of water can be expected where there are natural channels and storage basins in the‘. K. weathered:Li‘ "L“V‘ unit.zone, such as are formed where barriers of unweathered rock cross otherwise\ LLH-’\_;“>; deeply1_ ' .,weathered”up. \mHujm.valleys. ) 21 Bore-holes that penetrate below the zone of weathering can hope to tap water only if they strike permeable bands, such as fracture zones, planes of discontinuity, etc. The following list, supplied by the Hydraulic Branch of the Public Works Departmentenumerates the bore-holes in the Mwingi area and their productivity: Depth Rest- Yield Bore-hole Number I Locality IcompletedDate I (feet) level (galls./ I I struckWaterat I I (feet) day) ---- i I I I I I 96 .. .. 1930 297.: 1633H: 154l‘ 960 Mwingi I w" , 1- C.104 .. .. Mwingi 1940 297 ? 27 4,560 I SA. 56 .. .. Mati R. 1940 253:53 - Nil SA.92 .. .. N.ofGai 1941 156[5h - - Nil C.696 .. .. GaiNo.1 1948 534<1.” I 250I‘M 220I‘M 2,880 C.1583 .. .. Gai No.2 1951 3011m 1481;\ 123:f. 1 3,480 C.134H ..V, ..V. Tumboni 1940. 1 2752—5 168h‘ 1685‘ 600 C.573, ‘ , V Waita\mtm 1947Wm“ 500WM 66m I 158:\ 1 1,920 No.1\H, i (C.617,MT ...V ...V I Waita“'3t W471947 435 I 140;UN: 4:5425 I 1203:0 I TIN)7,201) No.2\L‘ C.919i ‘45” ..> ,, \gpmgfl ‘Ula1949 308Uh "M ‘\H 1504H . "m! I Ngomeni I 170; 250 I 114,760 The“u" vimsites Hfof Hmthe MH’C~?:HM\bore-holes mmhave inH: mmlmost (nocases Fri}:been inwalcdinserted n21on Hitthe Hhig‘map huntfrom :qgeo- graphical Ummiixmlrxco-ordinates \Lipmiuisupplied byin themy HydraulicHuimuht Branch,Bumd‘u andumi shouldmmfld bybe regardedrcgnu‘dui mas uonly .:I‘}‘:'.\\tt1h1£Lhapproximate. IX-REFERENCES!\ RF}5l-1Rli\'( PS *Barrow,BLI‘IL'M. G.,(1‘. 1912.-HTheMil, "Hutu-n11:GeologyH. ofw LowerA w w: DeesideIkcmic andMid theZ‘M‘ SmuSouthernflicw Highlandnh‘umi Border."[3:‘1x‘.\'1'," Proc.f’v‘m‘ Geo/.(n'm’, Assoc.,{mm H Vol.\M, XXIII,\\IT§. pp.PD 247-290.J“ :‘JU, ; Bear,Ham." L.i, M.,\!V 1952.-H1‘5 I, “>\A gm‘it‘tigk:geological ReconnaissanceRcovwxmumgg wof theHy area“Tm South-eastStuwi'izml ofn“ Embu." ReportRu;m:1\'uNo. 23,:HLm‘i1 Geol. Surv.Sm". Kenya.{\um Brown,Hum-.11. W.\\, H.,H” 1906.-HAI‘M“: “\ .MHLTKQ,Journey to:L‘ the:q Lorian10mm Swamp,Simi‘n‘l‘, BritishHtflixl‘ EastFm! Africa.".\M'fm,” (nagGeog. Joum.,lJm/.r_ Vol.\HI, 27,:7, m“,pp. 3"36-51.51, Dixey,Dzwf‘. F.,I . 1948.-HGeologyI‘M“, "('vcnlng} ofw! Northern\n"1hcr':1 Kenya."fxcmu. ” ReportRugmrl No.\u 15,if Geol.Us". Surv. Kenya. Groves,(W'\. A. W.,\\ 1935.-HTheHHS, "Thu charnockiticdiutwgkitg \cr'icxseries of Uganda,L gu-m Britishmam East"m Africa."\"’:c:‘ “ {JuanQuart. Journ.m Geo/. Soc.,x V. London,lu.m1»‘m.\nVol. flXCI,\( Lynpp. 150-207.m :w‘. Harker,Haiku. A.,~\._ 1950.-HMetamorphism."BUSH. "\lcl‘mww?hixn‘," 3rd«:11 Ed.id, Hatch, F. H.,1L. and Rastall,RLLxLuL. R. H.,H.. 1950.-HTheMFR ”I‘m Petrology[’x'imh ". H?[:1C5L\IHJLHAL‘_\of the Sedimentary rocks."«MAN, 3rd,‘ . Ed., revisedV byn} M.\1, Black.Blank . Hatch, F. H., Wells, A.»\ k.K. miand \ms.Wells, \1‘M. K.,.K , WmI949.-HThe“I m m-mPetrologyg; of :cthe Igneousigruurx Rog-oRocks."“ 10th Ed. Holmes,HuEmu»._ A.,\. 1918.-"OnWIN. “()H them.- Pre-CambrianI’I‘Lukumhrnw‘ and Associated\wm' m1 RocksRuck» ofm” theHm DistrictI):~H':ct 01'of Mozambique."hfi/unnimzuc.” Quart.U:‘r:.’=‘:'. JOllrn.‘lwu‘u Geo/.(1‘ Soc.,.Sm H London,I nmimx Vol.\ u“ LXXIV,I \\I\, pp.:‘p 31-98.F; m} MacGregor, A. M., 1947.-HAn'\:1()L11h:.rutOutline of the'1WL‘(:I{‘w"1\\~:Ei\’LL1Geological HistoryH‘wn'} n:of SSouthernmum-"m Rhodesia."!{?'.~afcxfk:.” Bull. No. 38, (ind.Geol. Suw-Surv. wv'n‘m‘Southern Rhodesia.R‘mmw}: Mining and Geological Department, 1935.-HAnnual19.15. "Airmm ReportPaw-Mt for1H: 1934."NH” GovernmentLiw'u‘xmr-am Printer,xicr. Nairobi.\Llll'u‘ni. *Not consulted in original...... i" 22 Parkinson, J., 1920.-"Report on the geology and geography of the Northern part of the East Africa Protectorate." Co\. Rep. Misc. No. 91, Cmd. 729. 1947.-"Out1ines of the Geology of the Mtito Andei-Tsavo Area, Kenya Colony." Report No. 13, Geo\. Surv. Kenya. Read, H. H., 1931.-"Geology of Central Sutherland." Mem. Geo\. Surv. Scotland. SaggersDn, E. P., 1957.--"Geology of the South Kitui Area." Report No. 37, Geo\. Surv. Kenya. Sanders, L. D., 1954.-"Geology of the Country East of Kitui." Report No. 30, Geo\. Surv. Kenya. Schoeman, J. J., 1948.-"A Geological Reconnaissance of the Area West of Kitui Town- ship." Report No. 14, Geo\. Surv. Kenya. 1951.-"A Geological Reconnaissance of the Country between Embu and Meru." Report No. 17, Geo\. Surv. Kenya. Shackleton, R. M., 1946.-"Geology of the Country between Nanyuki and Marala\." Report No. 11, Geo\. Surv. Kenya. Stewart, F. H., 1946.-"The Gabbroic Complex of Be1helvie in Aberdeenshire." Quart. Journ. Geo/. Soc., London, Vo\. ClI, pp. 465-498. Stockley, G. M., 1943.-"The Pre-Karroo Stratigraphy of Tanganyika." Geo/. Mag., Vo\. LXXX, pp. 161-170. Sutton, J., and Watson, J., 1951.-"The Pre-Torridonian metamorphic history of the Loch Torridon and Scourie Areas in the North-west Highlands, and its bearing on the chronological classification of the Lewisian." Quart. JOllrn. Geo/. Soc., London, Vo\. CVI, pp. 241-308. Temperley, B. N., 1938.-"The Geology of the Country Around Mpwapwa." Short Paper No. 19, Dept. of Lands and Mines, Geo\. Div., Tanganyika Territory. Thompson, A. 0., 1956.-"Geology of the Malindi District." Report No. 36, Geo\. Surv. Kenya. Turner, F. J., I949.-"Mineralogical and Structural Evolution of the Metamorphic Rocks." Memoir No. 30, Geo\. Soc. America. Walker, E. E., 1903.-"Reports on the Geology of the East African Protectorate.""C Colonial Office, Africa Cd. II of 1903. G.P.K. 1233-750-5/55 ~~~ bp:1yllitem'lst also be considered. Hitchen at Kinyiki (Parkinson, 1947, p. 33) considered that such veins originated from reconstituted hornblende rocks and that a passage could be traced through anthophyllite to magnesite at the surface. The serpentinization at Kamuthengi can be attributed to the action of late stage liquors and recrystallization under slight stress.