342 IAL REPORTS— MISCELLANEOUS. No. 91. EAST AFRICA PROTECTORATE. GEOLOG With §■1 REPORT 7 ~ = f ON THE ^ ^B| EOGRAPHY OF THE NORTHERN PART OF 7 J p SAST AFRICA PROTECTORATE, i s T the Gneisses and Schists of the District, by JOHN PARKINSON, M.A., M.Inst. M. & M. presenteD to lpacl.ament b£ Command of t)ts dfcajests, June, 1920. LONDON : PUBLISHED BY HIS MAJESTY'S STATIONERY OFFICE. To be purchased through any Bookseller or directly from H.M. STATIONERY OFFICE at the following addresses: Imperial House, Kingsway, London, W.C. 2, and 28, Abingdon Street, London, S.W. 1 ; 37, Peter Street, Manchester; 1, St. Andrew's Crescent, Cardiff; 23, Forth Street. Edinburgh ; or from E. PONSONBY, Ltd., 116, Grafton Street, Dublin. [Crad. 729] 1920. Price $d. Net. COLONIAL REPORTS— MISCELLANEOUS. No. 91. EAST AFRICA PROTECTORATE. INTRODUCTION. During the first year of the War 1914-1915, the writer had the opportunity of travelling through the Provinces of the Northern Frontier District and Jubaland which together constitute about 45 per cent, of the East Africa Protectorate, on a mission involving an examination of the geological conditions there obtaining with the object of augmenting the existing water supply. This Report deals with the Geographical and Geological results then obtained. Route Taken. Owing to unexpected difficulties of transport, a journey to Lake Rudolf, which was included in the Survey programme, had to be abandoned, and the very approximate Geological Sketch Map of that district is due to information kindly furnished by Protectorate Officers. In the Northern Frontier District, the expedition travelled from Nairobi to Fort Hall, and Nyeri, thence, skirting the northern flanks of Mt. Kenya, to Meru and Archer's Post on the northern Uaso Nyiro. The river was then followed eastwards as far as the Lorian Swamp, thence the track north-eastward to the district of Wajhir, and finally to Moyale on the Abyssinian frontier. From Moyale the Survey proceeded to Eil Wak on the borders of Jubaland, and, after retracing its steps, returned to Archer's Post from the former station, via Marsabit. Nairobi was reached by following up the Uaso Nyiro to Rumuruti and entering the Rift Valley near Nakuru. In Jubaland, two expeditions were made starting from Kismayu, the Provincial headquarters ; the first to a point some 40 miles west of Afmadu on the usual route to Wajhir, the second up the Juba River to Serenli and La Hele rapids, a distance by water of nearly 500 miles. The part of the East Africa Protectorate thus traversed falls into two natural sub-divisions : (1) The Northern Frontier District, and (2) The alluvial plain of Northern Jubaland. The former consists of hilly country composed of ancient crystalline rocks, partly covered EAST AFRICA PROTECTORATE. 6 by lavas, the latter embraces the low flat thorn land which commences at the Merti Plateau, includes the Lorian Swamp, extends eastwards to the Indian Ocean and northwards to the sandstones of the .Tubal and Series between Serenli and Eil Wak. 1. The Northern Frontier District. The physical features of the Northern Frontier District, which has an area of over 55,000 square miles, stand, in striking relation to the Geology.* Maps I and II. A short distance beyond the south-western corner of the distr.'ct, in the Naivasha Province, the rolling plateau-land which culminates in the piled-up lavas of the Aberdare Range is divided into unequal parts by the northerly portion of the East African Trough or Rift Valley, where Lakes Nakuru, Hannington, and Baringo lead on to Rudolf and the western border of the Northern Frontier District. (Fig. lay Travelling down stream and north-eastwards along the Uaso Nviro, the carpetting lavas which hide the gneiss below are left a short distance to the east of Rumuruti (6,000 feet above sea level), not again to be seen until about 60 miles in a straight line have been covered and the middle reaches of the river come into view. (Fig. 16). Between these two appearances the traveller makes, near Olloro- made, in little over four miles, a sudden descent from a height of 5,500 feet to a plain under 4,000 which drops slowly eastwards to Archer's Post, the Lorian Swamp and the sea, while the higher ground sweeping southwards merges into the northern slopes of Mt. Kenya. The lower plain is broken to the north and west by the heights of the Mathews Range, rising in Uaraguess to nearly 9,000 feet, of the Ndoto, rising to over 6,500, and the hills on either side of the Horr Valley, not far from the south-eastern corner of Lake Rudolf. App. C. Fig. a. The lava flows forming the borders of the Rift Valley at Laikipia and Rumuruti, the high gneiss plateau emerging from beneath their eroded edges, the rapid descent at Olloromade and the continuation on the lower level of the strongly marked gneiss hill region trending north-west towards Lake Rudolf are the most important features of the western part of the district. Fig. ii gives the profiles of the upper and the greater part of the middle stretches of the river and shows the more rapid fall in level at the locality "A." It is noteworthy that small swamps are rather characteristic of the plateau of the upper Uaso Nviro and the Seya, whilst the sharp descent * For an account of ilic Geology to the South, see 11. Brantwood Maufo. Col. Rep. Miscell. No. 45. Cd. 3828. L908. R I renoes to the principal reports and papers dealing with the Geology of the Protectorate are there given, to which, amongst others, should be added: ■"Studio Geologico sul materiale raccolto da M. Sacchi." Seoonda Spedizione Bottego, 1900. Presso Soc. Geogr. Ital. Also Cufino, I... " I Resultati scientific] della Mission,- st Eanini-Paoli n. 11a Somalia Italians Meri- dionale." Boll. d. Reale Soc. G< ogr. Ital. Ser. •">. Vol. 5. L916. \k sit. Parkinson, J., Geogr. Jour. 44. 1914. p. :>:?. Also Fritz Jaeger, Mitt, aus den Deutschen Schutzgebieten. Part 2. Berlin. 1913. C. W. Hobley, "The Alleged Desiccation of Easl Africa." Geogr. Jour. 44. 1914. p. 467. (bbt) Wt. 3k:796/354. 1,175. 6.20. B.&F. G. LI. 4 COLONIAL REPORTS MISCELLANEOUS. at " A " to another stretch having mature form suggests re- juvenation.* Subsequent investigation may show that the Uaso Nyiro originally continued its northerly direction towards the Mathews Range, instead of turning abruptly eastward near Olloromade to descend in a rapid- broken course to its middle reaches. The position and direction of one of the headwater streams of the Seya system is suggestive of this. The Uaso Nyiro can then be divided into three parts : an upper measured from its source to the sharp drop in level north of Olloro- made ; a middle portion including the descent from the highlands to the great plain of erosion of the Northern Frontier District, and the traverse of that plain, and, finally, a terminal portion, which winds as a sandy channel through a plain of another character, the great alluvial plain of southern Jubaland. Three types of country distinguish these three divisions : the first includes the cool open farmlands of Laikipia, the second the hot unfrequented sparsely forested rocky country of the middle reaches, the third the desolate waterless thorn scrub tenanted only by roving bands of Somali s and rarely crossed by a European. From Meru northwards, through the centre of the Northern Frontier District, isolated hills of gneiss surrounded by lava flows, extending from the northern flank of Mt. Kenya form characteristic scenery. These flows are not left until the Uaso Nyiro is reached, the river forming a dividing line, immediately to the north of which gneiss and other strongly crystalline rocks greatly predominate as far as the southern edge of Marsabit. At Archer's Post, around Laisamis and also in the south-east of the District at Chanlers's Fall and Merti, the greatly eroded surface of these ancient rocks is overlain by lava, the sculpturing of the whole giving a measure of the amount of erosion which has taken place since the flows were outpoured. As in the Rift Valley, the final phase of vulcanicity was obviously of the explosive type, and puys, often exceedingly well preserved, are locally not unusual in a country composed essentially of gneiss. App. C, Fig. i. Examples are conspicuous to the north of Laisamis and to the south of Merille, where also for a short distance the ground is thinly covered with volcanic ash, now consolidated into a layer incrusting the underlying rocks. It is clear that the north-west part of the East Africa Protectorate is characterised, no less than the south-west by volcanism, in fact lava fields cover about half of the area of the Northern Frontier District and volcanoes of enormous size form one of the most interesting features of this part of the Protectorate. The serrated mass of Kenya, so different from the almost perfect cone of the Kibo summit of Kilima Njaro, dominates the southern part of the district and is sufficiently well known, but attention * See C. H. Stigand and A. Holmes. Georg Jour. 48. 1916. p. 154. Also R. Fourtau, 'Le Bassin X antique.' Ann. de. Geogr. No. 155. 28 1919. p. 373. The elevation indicated by siuh a rejuvenation l- considered as more than local Near Olloromade the dissected edge of the slope is filled with alluvium at least 100 feet thick through which tune a channel with vertical sides. This is indicative of rejuvenation. The cba acter of the channe oJ the Turoka at its exit i'rcin tin western e ge of the Kapiti Plains mto the Rift Valley (Magadi Branch Railway] is closely similar EAST AFRICA PROTECTORATE. O should be called to the great volcanoes of the north, since but little information about them is available, due doubtless to their inaccessibility. The greater part of the volcanic country traversed by the Survey is composed of lava flows, of which the vents of origin are not now apparent and which may be taken as a whole to be older than the volcanic phase, the active remnants of which still exist south of Lake Rudolf.* A broad distinction into old lavas| capping the scarps and into newer rocks on lower levels is easy to make : thus to the south of Merille and to the east of Archer's Post the latter are readily distin- guished by their more marked blackness, their rougher more irregular and scoriaceous surfaces, their usual ropey structure and by the fact that they support little or no vegetation. It is evident that they are of no great age. About two days journey northward of Merille and Laisamis are the lava flows which form the southern edge of the huge mass of the Marsabit volcano and thence stretch northwards almost to the Abyssinian escarpment. The more northerly part of the field is known as the Dido Gullgullo, a waterless expanse which is practically a flat plain, its surface thickly strewn with fragments of lava up to 4—5 feet across, representing doubtless the disintegrated remnants of the final flow. The rocks have the appearance of being older than the lavas of Marsabit. Individual outpourings are not seen until about 30 miles from the northern edge of the great volcano, when the ground becomes more broken by the in-coming of broadly columnar masses of olivine- basalt, which resemble petrographically many of the flows of the vent itself, and owe their source no doubt to the same centre of eruption. Approaching Marsabit from the north, the scarp which forms the front' er of Abyssina is still visible as a faint blue line, though nearly ninety miles of lava intervene ; the gneiss inlier of Turbi stands forwards from the Highlands, sentinel-wise, more firmly outlined, * e.g. Teleki's volcano. Compare Joseph Thomson. " Through Masai Land." London, 1887. p. 317, for the " most remarkable evidence of recent volcanic activity " at the northern end of Lake Baringo. J. \Y. Gregory makes a similar comment, Geogr. Jour. 4. 1894. p. 315. | The older lava overlying the gneiss and schist of Archer's Post Hill is a basalt with augite phenocrysts -25-*75 mm. long and a considerable quantity of magnetite set in a fine-grained base of- minutely granular augite and magnetite and laths of plagioclase with a noticeable quantity of colourless residual glass. Some small pseudomorphs of serpentine may represent original olivine phenocrysts. The " older " lavas to the north, as far as examined, differ immaterially. With tliis group we may class the olivine-basalt of Chanler's Falls. The rock is rather altered, dolomite is not luicomraon, magnetite is abundant. The rock contains an equal proportion of short laths of an acid labradorite and granular augite. The phenocrysts of olivine are much changed. Of the "newer" lavas that from the west side of Bambon Kop, east of Archer's Post, will serve as an example. Olivine, in two generations is more abundant than in the rocks described, the felspar as before is an acid labradorite. The slide is rather opaque, through the separation of an iron oxide in a glassy base, which contains minute crystals of augite and skeleton crystals of magnetite. 6 COLONIAL REPORTS — MISCELLANEOUS. to the north-west rises the long sloping mass of the Huri* volcano z in the far distance to the west Kulal overlooks Lake Rudolf : south- wards lies the forest-clad crater of Marsabit. In the middle distance and around, before and on either hand stretch the seeming endless lava flows, their dismal, waterless, trackless monotony broken only by rare cones of ash. The Marsabit volcano is„of great interest. The map of the district made by Mr. Archer, C.M.G., now His Majesty's Commissioner in Somaliland, shows the volcano to be elliptical in plan, the longer axis trending in a north-east and south-west direction. The base is about 40 miles long by 30 wide. The greatest height of the flows forming the body of the volcano is approximately 4,500 feet above sea level, the surrounding plain is about 2,000 feet, hence the slope of the cone along the major axis is only 1° 21'. Considerable erosion has taken place since the outwelling of the lavas which built up this singularly flat cone ; the columnar basaltsf of the eastern side have been cut through to a depth of about 100 feet, but an important fragment of the crater wall still remains and the age, as already remarked, is most probably less than that of the flows to the north. Eleven days were spent on Marsabit and a journey made round the southern and south-eastern parts of the mass as well as the north. Except on the northern flank, ash beds are uncommon, and there seems no doubt the volcano was produced by successive outpourings from a central vent, which slowly built up by a process of accretion, the huge flat cone, sufficiently interesting in itself and in the abundance of its vegetation and animal life in very welcome contrast to its surroundings * See Count Wickenburg's journey from Jibuti to Lama. G-eogr. Jour. 22. 1903. p. 699. Huri, "A continuous chain of conical bills, rising to some 5,000 feet, runs from N.E. to S.W. for 50 miles." See Peterm. Mitt. Nos. 9 & 10. Jabrgang 1903. Taf. 19-20. f Characteristically the lavas contain phenocrysts of olivine and augite, occasionally 5 mm. long, the former showing peripheral alteration. The felspar is usually an acid labradorite. A little residual glass may occur and occasionally a noteworthy quantity of magnetite granules. The rocks are fresh in appearance, the translucent felspar forms crystals about •15 mm. long, the augite which accompanies it in the base is granular to prismatic in habit. The columnar flow on the S. side of the Dido Grullgullo, N. of Marsabit, is a similar rock containing purplish-brown a unite, opbitic towards the labradorite. A phonolite from the west side of Marsabit contains phenocrysts of nepheline occasionally 3-5 mm. long. A thin section shows the mineral to occur in two g< nerations, ih smaller having an average size of -03 mm. and forming a marked proportion of the bast which is cryptocrystalline with minute scattered laths of felspar. A rich grass-green pyroxene (aegerine) is conspicuous. At Ret, on the south side of the volcano, columnar and spheroidal struct urc is excellently shown. The preponderance of olivine-basalts in the northern half of the Protectorate in comparison with their rarity near Lake Magadi, and the prevailing nepheline-syenites of Mt. Kenya is of considerable interest. From the Lake Magadi district olivine was abs< nt in the basalts examined. Judging from the specimens collecteel in the Northern Frontier District, alkaline rocks form an insignificant proportion of the lavas as a whole. Prof. Gregory has described trachytoid phonolites from Marsabit. (Donaldson Smith. Appenelix E. p. 423. "Through Unknown African Countries." 1897.) EAST AFRICA PROTECTORATE. / In regard to the main crater, the usual camping ground close to the spring known as Uelamere's Njoro lies on the edge of a grass-covered plateau of lava and at the base of a densely forested crescent-shaped hill, which may possibly be resolved into three arcs of progressively diminishing size, representing as many craters. The ground is greatly broken, and without detailed mapping it is exceedingly difficult to be certain of the structure, especially as the forest hides any view which might otherwise be obtained. The crater lake of Marsabit, about 800 to 900 yards in diameter, and a second, now a mere swamp, near to Delamere's Njoro, appear to lie between the two outer rings. This later, more explosive phase of vulcanicity gave rise to a large number of puys built up of mingled lava and ash, which stud the edge of the central plateau and give a characteristic serrated outline to the volcano when seen from a distance, a peculiarity shared with Huri.* App. C. Fig. b. This phase also produced certain small craters with vertical walls and no cones resembling the " pit craters " of Hawaii, described by Dalyj- which he considers were formed by " melting perforation," an explanation which seems applicable to those of Marsabit, when the resemblance between the Pacific and East African volcanoes is taken into account. In consideration of the waterless nature of the country for several days in any direction from Marsabit, it is interesting to record the presence of fish in one of the streams on the south-east flank and the almost universal occurrence, wherever there was water, of a large number of gasteropods. Dyke rocks on Marsabit are rare, one cutting through the side of a tuff cone proved to be an olivine-basalt. Turning to the north-central and extreme northern parts of the Northern Frontier District, a general conception of the structure of the country can be obtained from Topeisa, one of the numerous spurs which jut from the Abyssinian Highlands southwards. To the west a plain of gneiss and schist covered with thorn scrub lies 1,300 feet below the observer, but passes rapidly southwards beneath the dominant lava fields : to the east the old crystalline rocks form more broken country, rising here and there into low hills, before the borders of Jubaland are reached and they sink beneath the sediments of the Coastal Belt. The suddenness with which the deeply incised edge of the Abyssinian Highlands rises from the plains to form the so-called " escarpment " is very striking, but except for this abruptness, it is not obvious that the feature is due to a fault. The rapid amalgamation of the parallel ridges which stretch from the higher ground, like fingers southwards, and as isolated hills are the most prominent features of the southern * Huri is inferred from this peculiar outline to be a volcano of a similar type to Marsabit. It was not visited. | " Igneous Rocks and Their Origins." 1914. p. 141. & tic 96. p. 142. Compare C. W. Gwynn. Geogr. Jour. 38. 1911. p. 123, where the lines of craters S. of Lake Stefanie are mentioned. He says, of the Ciorai group, these "are especially curious, notably Dillo, hardly slewing a projecting rim above the level of the ground, but forming cliff lined pits some half mile in diameter and several hundred feel deep." 8 COLONIAL REPORTS— MISCELLANEOUS. plain, produces the effect of these highlands having been built up by a process of coalescing of outlying eminences, which is not the effect of a fault. Also, stripped of valley alluvium, locally of considerable thickness, the dissected edge of the highlands would be still more apparent, hence if faulting has contributed to the production of this feature, it was most probably of an age greater than that of the majority of the faults of the Rift Valley system. It will be noticed as one of the principal characteristics of the District, that a broad belt of low ground lies between the Abyssinian frontier on the north-east, and the Mathews and associated ranges on the south-west, and passes into the alluvial plain of Jubaland. Map II. Its western and north-western continuation includes Lakes Rudolf and Stefanie, and the whole would be much more marked if the compara- tively recent growth of Marsabit and the neighbouring lava flows were neglected. The trend of the Nyiro and Ndoto hills, south-east of Lake Rudolf has an interesting parallelism to the Abyssinian escarpment, south-east of Lake Stefanie, to extensive escarpments west of Lake Rudolf recorded by the late Capt. R. H. Leeke* and to the still more westerly Kuku escarpment between Nimule and Gondo- koro.f The late Major Stigand inclined to the belief that the slope of the General Mathews Range to the level of the Elgess is a fault scarp.J Noteworthy in this connection are the remarks of Blanford§ who records the presence on the Abyssinian Plateau of Bathonian and Astartien Beds, the Calcaire d'Anatalo, outcropping at a height of 2,600 metres at Gamma and again at 400 kilom. to the south at 1,800 m. H. Douville remarks that the Jurassic formations of Abyssinia are nearly horizontal, or at least plunge gently to the south. In British East Africa, on the Juba River and the Uganda Railway, Oxfordian Beds appear raised only a few hundreds of feet above sea- level. An important post-Oxfordian uplift is implied in the north, resulting in the formation of the Abyssinian Plateau ; whether this could take place without peripheral faulting appears doubtful. As far as it goes the evidence from the Stefanie region is corrobora- tive of a faulted margin. Maud describes || the Goro Escarpment as a " great natural feature," and states that it continues in a broad sweep as far as Gaddaduma. Donaldson Smith describes the ground west of Mega, a volcano lying to the east of the Goro Scarp, as a precipice. * "Northern Territories of the Uganda Protectorate." Geogr. Jour. 59. 1917. p. 201. Map. t Major C. II. Stigand & Dr. A. Holmes. Geogr. Jour. 48. 1910. p. 147. Map. J Private communication. §W. T. Blanford. Quart. Jour. Geol. Soc. 25. 18G9. p. 403. Aubry. Bull. Soc. Geol. de France. 3ie. ser. 14. 1886. p. 201. Douville. p. 240. Also Blanford. " Geology and Zoology of Abyssinia," London, 1870. || Geogr. Jour. 23. 1904. p. 552. A very broken " sweep " as alr< ady noticed. EAST AFRICA PROTECTORATE. 9 Lake Stefanie itself is described by Suess as being in " eine weitere Grabenformige Senkung."* The evidence on the whole, though inconclusive, is in favour of an old fault circumscribing, in part, the southern edge of the Plateau. The Uaso Nviro is the only permanent river in the Northern Frontier District, but drainage channels proving the former existence of others, equally if not more important, occur, and of these three systems are sufficiently remarkable to warrant a few remarks. The channels known as Lak or Lugga are dealt with later. Concerning the first two of these extinct or almost extinct systems, but little can be said as they were not seen by the Survey and are only mentioned for the sake of completeness and because of their importance as being the basis of the water supply. For information concerning them I am indebted to Major AthiU, R.A. In regard to the first, the Seya after traversing the higher ground north of the Laikipia Plateau is joined by an important tributary, the Nyeng, rising on the south-west flanks of the Mathews Range, and is mapped by Major Athill as flowing through that prominent ridge in a north-east direction and loosing itself towards the Elgess. The second system, perhaps more important, is the Balessa. The word probably signifies a water-hole and the country round the northern Horr, south of Dabandabli, is known to travelling natives as the " Balessa," because of the many water-holes it contains. In general terms, it is the country north of the Elgess and Koroli desert. The gathering channels of the system are in the southern Horr valley, between Mt. Nviro and El Donyo Mara, where permanent water is found in the headwater streams, which, however, do not join if the rains fail. Thence the channel passes round the S.E. and S. flanks at Mt. Kulal and dies out to the south of lat. 3° 30' in the series of water-holes aforementioned. Major Athill puts forward the probable suggestion that the " Balessa " plain extends northwards to include Lake Stefanie. The third line of drainage, like those preceding, is northerly, the head channels rise not far north of Archer's Post and thence follow the grain of the country as given by the foliation of the crystalline rocks through Kauro and Kinya, where the valley is about 25 and 100 yards wide respectively, to Langaia where it passes along the western edge of a low escarpment of gneiss capped by lava. At Merille an important tributary is received from the west, and shortly after, before Laisamis is reached, the valley, now greatly broadened, turns abruptly in an easterly direction, as a flat-bottomed thalweg with lava-capped cliffs of gneiss, 300 to 400 feet high on either hand, very noticeable to the traveller on the ordinary " safari " road. At Laisamis a second large tributary from the west trends * ; Die Briiclie des ostlichen Afrika." Denkr. k. Akad. Wiss. Wien Math, natur. Classe. 58. 1891. p. aT-t. Compare " Les Fosses de I'Afrique Orientale d'apres Emm. de Martonne, "Traite" de G-6ographie Physique." Paris. 1909. p. 487. Fig. 219. Quoted also in " La Face.de la Torre.'' t. 3.3ie. p. 971. A faulted sunk-land is Inn shown trending from the country between Lakes Stefanie and Abbai in a general south-east direction. (G66) b 10 COLONIAL EEPORTS — MISCELLANEOUS. eastwards over ridges of felspathic gne'ss, and presumably joins the Kauro-Merille system.* As these now dry channels provide all the available water by means of shallow pits dug in the sands of their beds, except occasional springs, they are of very considerable importance in the development of the country. Before passing on to the sediments, a few remarks may be made concerning the crystalline rocks. These fall into two broad divisions : (a) a group of orthogneisses which show the usual characteristics of the intrusion, brecciation, veining and the like of a basic rock by one of acid composition (Abys- sinian frontier, W. of Moyale, and various localities on the Uaso Nyiro, especially W. of Archer's Post) and, (b) a series of completely metamorphosed sediments varying in composition from marbles to quartzites (Ajow) and quartz-schists. In the accompanying Note the hornblende-gneisses and schists are separated as a third group. The metamorphosed sediments are most fully developed in the north- eastern part of the district at Buttellu, where extensive beds both of marble and of quartz-schist occur, and also south of Marsabit, along the caravan route from Laisamis to Kinja, where, however, marble is a very subordinate member and the dominant rock a compact felspathic biotite-gneiss. Marbles and graphite-schists occur also on the upper part of the Uaso Nyiro, the former conspicuous a short distance to the west of Olloromade. From small boulders and fragments picked up on the hill sides similar rocks probably will be found both east and west of Archer's Post. The series is of importance in British East Africa.! South of Marsabit and near Laisamis, these rocks are associated with hornblende-schists. Among the intrusive rocks a serpentine found 15 miles X. of Debell (S. of Moyale) and an olivine-gabbro from the N. bank of the Uaso Nyiro, W. of Chanler's Falls are worthy of note. An old-looking granite, locally gneissose and containing microcline occurs a short distance N. of Ajow ; but taking the district as a whole intrusive rocks are rare. 2. The Alluvial Plain of Northern Jubaland and the Associated Older Sedimentary Beds. East of the great lava flows- of the Dido Gullgullo, towards Wajhir, the country consists of a monotonous plain of much eroded crystalline rocks, hidden often by patches of alluvium, dotted -with struggling thorn trees, intersected now and again by the dry sandy beds of former rivers and broken only by parallel, abrupt and isolated ridges. It is thus, save for the absence of puys and lavas, very similar to the gneiss country found south of the Marsabit volcano as far as the Uaso Nyiro at Archer's Post. Continuing still further south and east a striking * The Laisamis-Menllr system is mapped by Donaldson Smith as joining the Uaso Nyiro about 8 miles below Chanler's Falls. "Through Unknown African Countries." Mr. Archer concurs in this. Geogr. Jour. 42. 1913. p. 422. j Mr. C. W. Hobley, C.M.G. notes that, outside this district, marble occurs \. of Muinoni, on the Xzi River, E. of Thumbi and also W. of Voi. Probably these rocks may be referred to the same Series. EAST AFRICA PROTECTORATE. 11 change takes place depending on the disappearance of crystalline and igneous rocks and their replacement either by sediments of various kinds, oi' by a featureless plain of sand and loam. The dividing line passes from the Merti Plateau, on the northern bank of the Uaso Nyiro to the western part of the Wajhir district, and continues thence northeastwards to the west of Eil Wak. Travelling along the Uaso Nyiro. the immediate alteration in the character of the country experienced on leaving the Merti Plateau is very striking. This feature, one of the most remarkable of the district, composed of gneiss and capped by lavas, rises abruptly from a monotonous plain of soft brown silt to a height of GOO feet above the river (Draco- poli).* Beds of old alluvium containing well-rounded quartz pebbles occur on its flanks. To the west, crystalline rocks of many kinds give a broadly rugged character to the country, the Uaso Nyiro flows hemmed in by rocky walls, forced here and there into picturesque falls and rapids ; to the east the alluvium which forms its banks continues uninterruptedly in an unbroken plam to the Indian Ocean, unrelieved by aught save minor undulations, its desolation emphasized by stunted almost leafless thorn trees. It is worthy of note that in passing the eastern end of the Merti Plateau outstanding portions from the main mass become visible, in appearance strongly resembling the stacks detached by marine erosion from the cliffs of a shore line. Upon the available evidence^ the conclusion is drawn that since or at the time of the extravasation of these lavas, the sea has extended westwards as far as long. 39° in the 1st N. parallel and that the alluvial plain of Jubaland is the raised floor. This is equivalent to an elevation since that time of about 400 metres (1,300 feet). Turning northwards from the Lorian Swamp we find at Wajhir the monotony somewhat relieved ; outcrops of a friable earthy limestone or of a calcareous sandstone rise through the surface covering of red sand and mark the beginning of the sedimentary beds, which here no doubt rest directly on the crystalline series. As far as present knowledge allows, the sedimentary rocks of the northern part of the East Africa Protectorate fall into the following groups. (i) The Jubaland Series. (ii) The Eil Wak Limestone and the Wajhir Beds, and (iii) The alluvium and raised coral reefs of the Coast. The older reefs are probably to be included in group ii. (i) The Jubaland Series. These beds which appear first on the Juba Eiver between Heilishid and Lawita, consist typically of blue shales or mudstones having a characteristic conchoidal fracture and weathering into lens-shaped fragments. With these are associated thin reddish sandstones. * G-eogr. Jour. 42. 1913. p. 137 & Map. Also A. Arkell-Hardwiok, "An Ivory Trader in North Kenya,"' Longmans. 1903. p. 245. 12 COLONIAL EEPORTS — MISCELLANEOUS. West of Eil Wak, sandstones, often ferruginious,* predominate, and near the contact with the crystalline rocks the beds are pebbly arkoses, frequently false-bedded. In both localities thin beds of pale grey limestone occur crowded with fragmentary shell remains. Wherever seen these strata were but little disturbed ; the dips observed showed that the beds were gently undulating about a N. and S. axis. App. C. Fig. e. The late Mr. 6. C. Crick, of the British Museum of Natural History, who examined the fossils found, stated that the ammonites were of Upper Oxfordian age.j - See Appendix A. (ii) The Eil Wak Limestones and the Wajhir Beds. Taken as a whole, these sediments together with those of Serenli and the Juba River consist of cream-coloured earthly limestones or friable calcareous sandstones, in many places containing much gypsum and showing little or no indication of bedding. The Eil Wak limestone proved unfossiliferous where seen, but from Wajhir Mr. Bullen Newton has identified a Bythinia and a Planorbis, " not specifically determinable." Deternr nations which Mr. Newton has kindly made from other fossils, which on the whole are probably xather younger, are mentioned in connection with the localities where the shells occur and are followed by a short report which he has drawn up on the material submitted to him. In addition to the Lacustrine Beds of Wajhir, a fresh-water limestone occurs at Archer's Post and locally reaches the thickness of about 100 feet. From this deposit Mr. Newton identifies Melania tuberculata and Limicolaria rectistringata. A short distance below the station, this deposit is associated with fine silts and some ash beds, the whole showing that a small lake existed along this part of the river, its length being considerably greater than its breadth. The oldest record of the Uaso Nyiro found consists of a patch of large and well-rounded quartz boulders at a height of about 150 feet above the present level of the river. ^This deposit, no doubt, is older than the plateau lavas at that point. Fig. iii. At a relatively low level are a series of well-marked terraces which indicate stages in the draining of the lake. Proceeding down stream for 40-50 miles, the river drops about 150 feet forming a series of cascades known as Chanler's Falls, which cut across the grain of the banded ortho-gneisses of the bed. On the southern and in a less degree on the northern bank, lava overlies the gneiss, indicating that the waters of the river were tem- porarily dammed and shallow lakes formed to the west. The upper terraces near Bambon Kop (E. of Archer's Post) contain multitudes of Melania tuberculata, which, as the travertine weathers strew the ground in thousands, while on the bank of the river these are associated with large numbers of Planorbis. *At Lakka Dima, quartz -ran-, often very irregular, about -24 mm. across, in an opaque brow o c< ment. fAbs. Proc. Geol. Soe. No. 980. Nov. 25th. 1915. p. 6. See also "Through Unknown African Countries." 1897. Appendix F. the late Gr. C. Crick, " On tin I phalopoda from Somaliland collected by Dr. Donaldson Smith." p. 426. EAST AFRICA PROTECTORATE. 13 In addition to lakes now extinct, it appears probable that the existing swamps were formerly of greater extension. This is the case with both the Lorian Swamp and the Deshek Wama. In regard to the former, shells of AmpuUaria speciosa and Lanistes carina! us occur in great profusion on the silt within a few miles of the river, but at least 20 miles west of the edge of the swamp ; ground where now are kraals of the Boran and scrub of stunted thorn trees. Similar evidence, though not so pronounced, was noticed around the edge of the Deshek Wama. Without, however, observations extending through several rainy seasons it is difficult to say how much weight should be placed on such facts. Shells of AmpuUaria ovata and Lanistes carinatus were found on the flats W.S.W. of Moyale and a short distance E. of Turbi fragments of Leptospatha spathuUformis and Corbicula flu menalis . In dealing with Jubaland from the administrative or economic standpoint, the chief problem is, of course, the water supply, and in this connection the system of normally dry channels by which the country is traversed becomes of interest as holding out hopes of successful exploitation. Such a drainage line is known as a Lak or Lugga, and a considerable divergence of opinion exists among travellers on the amount of surface water any one may periodically contain, the frequency of surface flows and the passage of underground water. These important details await connected observations before definite conclusions can be reached. For the sake of clearness, two main systems of these laks may be distinguished in an exceedingly complicated network of channels : a more southerly, which is the easterly continuation of the Uaso Nyiro onwards from Madoleh, this is known as the Lak Dera, and a more northerly, the system of the Lak Jira, which receives many branches south of Wajhir, which with a general south-easterly trend joins the Lak Dera immediately to the west of Afmadu, and which may be continuous north-westwards with the Lak traced through Gerifta, Eil Lass and Buna. The Laks Dera and Jira, thus joined, continue under the former name to the swamps called Deshek Gumbi and the far larger Deshek Wama, whence rather obscure channels lead to the Juba River. The slopes which indicate the approach to one of these dry water- courses are typically very slight, banks in the ordinary sense scarcely exist, the bed of the channel is overgrown with vegetation, so that the line of drainage is usually distinguished from a distance by a belt of trees, more closely growing, of greater height and more abundant foliation than the scattered thorn trees, which elsewhere emphasize so forcibly the monotony and aridity of the land. App. C, Fig. d. Although surface flows do take place, for one was seen by the Recon- naissance, the water moving at the rate of several miles an hour and being several inches ; or even in some channels a few feet deep, yet the local nature of the rainstorms, the extremely slight grade, and the pervious character of the bed of the Lak, taken in conjunction with a very high rate of evaporation,* render it almost impossible that such surface movements can be maintained for long. * Some experiments were made to determine what this rati' was. They were not, however, considered conclusive, although there is no doubt the rate of evaporation is very high. 14 COLONIAL REPORTS — MISCELLANEOUS. No evidence was found to show that surface flows take place annually, but the wide distribution and commonness of the shells of Ampullaria and Lanistes, as well as several other genera of fresh-water molluscs, and the presence of crabs in the Lak Jira, at least, go far to show that surface water does in fact occur with some frequency. As the expedition traversed much of this country during the dry season, and the distribution of the rainfall and its amount are unknown, the following data, furnished by Mr. V. G. Glenday are of special value. He notes that on the plains, as distinct from the edge of the Abyssinian Highlands, the rains vary greatly from year to year in their distri- bution ; the " big rains " take place in April, May, and possibly June, the " lesser rains " in October and November. January, February and March are generally very dry and very hot. Assuming the average rainfall in the plains to be the figure for Moyale for these three opening dry months of the year, the rainfall would be 4-30 inches for 1915 and 6 - 84 for 1916 as compared with total rainfalls at Moyale of 3O70 and 35 - 02 inches respectively. At Moyale in 1915 the heaviest falls in one day for March, April and May, were 1-72, 1.20 and 1*35 inches the total rainfall for each month being correspondingly 4 - 30, 6 - 90, and 4 - 55 inches. Mr. Glenday records in one day a fall of 3-48 inches (September, 1916), the total for the month being 3*95 inches. This storm was felt at Buna, 55 miles to the S.E. of Moyale, not so heavily, but sufficient for water to come down the channel as a wave. It should be remarked that this Lak is a sandy expanse of considerable width, which furnished at the time of the visit of the Survey in December 1914 sufficient water for the maintenance of small herds of cattle. All the wells seen by the Survey, except Wajhir, were either dug on the banks of one of the principal lakes or on one of their innumerable ramifications. The word " well "is, however, a misnomer, for these excavations are in the great majority of instances little better than shallow pits, or at best, irregular shafts of cross sectional area very disproportionate to their breadth. At Wajhir, on the contrary, true wells are found, three feet to three feet six inches in diameter, excavated in a compact calcareous sandstone to a depth of about 40 feet. This group of wells extends over an area of some 240 square miles and provides water, which is not very unpalatable, except at Eil Tuli at the eastern end of the district. At Eil Wak, to the north-east, the water is exceedingly unpleasant. At this important halting ground the cavern-like wells are dug in compact, fairly hard rocks, light greenish-grey to brownish-grey in colour, very largely composed of gypsum, in crystals up to 50-60 mm. long with locally a carbonate in minute grains or more rarely in rhombs, about -03 mm. long. The late Lieut. Aylmer* in a careful and instructive paper records " coral limestone " in the neighbourhood of Eil Wak ; this was not seen by the Survey, who, however, did not travel far from the wells. These highly gypsiferous beds indicate the * Geogr. . Jour. 38. 1911. p. 293. At Eil Tiili, Salkeld notes in descending order, gypsum, clay, black sand, stones and hard white sand. The black sand is impregnated with sulphur. Geogr. Jour. 46. 1915. p. 52. EAST AFRICA PROTECTORATE. 15 desiccation of a lagoon,* a noteworthy extension of the sea, which possibly at this time carved out the Merti Plateau. In regard to the origin of the water in the wells at Wajhir, the presence of freshwater shells (Bythinia and Planorbis spp.) in the limestone of the neighbourhood demonstrates the existence of a lake at a former period on the edge of the crystalline platform. Such a lake, destroyed by desiccation and siltkig might, the directions of drainage remaining unaltered, continue to be an area of shallow sub-surface water, irregular and variable though the feeding sub-surface supplies would be. Such feeders would include the Eil Lass — Gerifta lak. Other evidences of desiccation may be mentioned. At Buna the large lak, already referred to, provides exposures of ill-defined strata, formed of angular quartz grains loosely cemented by calcareous material and containing abundant individuals of Cleopatra bulimoides, Corbi- cula flumerialis, Ampullaria ovata, Leptospatha spathidiformis and Melania tuberculata, many of the Corbiculae having the valves still united by the ligament. Of other areas where water must formerly have existed in abundance, that of Chukali Ghofu, 30 miles to the west of Eil Wak on the borders of Jub aland, was the best example found. Here on a surface of fine brownish-coloured silt lay concretions of calcareous mud, usually hollow and showing a well marked concentric structure. From these Mr. Newton identifies Melania tuberculata, Cleopatra bulimoides, Rhacis rhodotaenia, Corbicida radiata and C. flumenalis. The occurrence of a few pebbles, often well rounded, indicates the former existence of a river. Other evidence of progressive desiccation is afforded by the wells, winch are frequently found, when in crystalline rocks, in positions where no native would sink unless some surface indications of water were present to guide him. Of these, the well at Ajow is an excellent example. Water is now obtained from the bottom of a slightly inclined shaft or pit formed by the removal of broken masses of quartzite. It is at the apex of a straight steep valley, the bottom thickly strewn with loose masses of rock, clearly once brought down by a stream of spasmodic, torrential habit. A " bed " of greatly weathered micaceous gneiss, almost in the condition of a clay, can be traced across the valley head immediately below the well, and it is probably due to tins that the water contained in the crevices of the rock forming the hill was held up, and in the past gave rise to a spring. This spring attracted the natives to the place, * See " Data of Geochemistry " 3rd Ed. U.S.G.S. Bull. 616. p. 211 & 576, also Mr. Bullen Newton's remarks, Abs. Proc. Geol. Sue. Nov. 25th, 1915. p. 7. See Appendix B. His note on Lake Assal in French Somali- land may be amplified by Aubrey's statement (Bull. Soe. Geol. de Fr. 3ie. Ser. 14. 1886. p. 201) thai near the Lake arc deposits of gypsum and salt, and that the beds containing freshwater shells are underlain by " cinerites Biliceuses avec diatomees." The Lake thus recalls in its deposits both those of Eil Wak and also of the former sheet of water occupying the Rift Valley, now traversed by the Magadi Branch Railway, where, and at Kijabe, extensive beds of diatomaceous earth exist. See also Toula (Denkr. k. Akad. Wiss. Wien. 58. L891. p. 553) for an occurrence of diatoms near Lake Rudolf, and sketch geological map of country from Kilima Njaro to X. of Lake Rudolf. 16 COLONIAL REPORTS — MISCELLANEOUS. and they, as the water gradually failed, followed it downwards until they reached the present depth of forty feet. A i Buttellu, a few miles to the south, where a similar dry river bed has cut its way through the same series of crystalline rocks, two wells doubtless owe their existence to former springs. In regard to the Juba River, as far north as La Hele, the course is that of a very mature stream. The rapids are about 80 miles north of the first appearance of the Jurassic rocks on the river, measured in a direct line. The numerous and sharp-angled bends, the prevalence of sandbanks, and the general shallowness of the water makes navigation difficult, even for those months of the year during which it is possible. SUMMARY. As far as the evidence goes, the following summary gives approxi- mately the sequence of changes. (a) Early and prolonged erosion. (6) Eruption of plateau lavas. Formation of the Rift Valley. (c) Lacustrine and fluviatile period, with continued erosion, the sea reaching to Merti. Lagoons of Eil Wak. (d) Volcanic (explosive) phase. Elevation of the sea floor to form the Jubaland Plain. Drainage of lakes. Desiccation and modern topography. In other words, subsequent to the eruption of the early lavas a fluviatile, lacustrine phase existed, both inside and outside the Rift Valley, during which the Jubaland Plain was covered by a shallow sea. This was followed by a later phase of elevation and slow desiccation, distinguished by the formation of smaller volcanoes and puys. Doubtless no hard and fast divisions can be true ; in general terms the making of the Rift Valley preceded the lacustrine phase, although evidence exists in the Lake Magadi district that some minor faulting took place during or subsequent to the existence of the lakes, while the slight erosion of the scarps suggests that there some, at least, of the faulting was later in the south than in the north. March, 1920. John Parkinson. APPENDIX A. From Abs. Proc. Geol. Soc. No. 980. Nov. 25th. 1915, p. 6. " Mr. G. C. Crick stated that the Cephalopoda subrnitted to him by the Lecturer consisted chiefly of crushed ammonites from dark-grey shales at Kukatta on the Juba River (lat. 2° 8' N.), there being also a belemnite preserved in a yellowish-brown rock-fragment from Serenli on the same river and somewhat north of Kukatta. He regarded all the ammonites as referable to Perisphinctes and its. section Virgatosphinctes, and to species which had previously been EAST AFRICA PROTECTORATE. ii described from the neighbourhood of Mombasa.* From this assem- blage of forms he concluded that the shales at Kukatta were of Upper Oxfordian (Sequanian) age. He stated that the belemnite from Serenli indicated the presence there of a slender -Milcate form, similar to those previously recorded from British Somaliland on the north, and from the neighbourhood of Mombasa on the south ; but, although of Jurassic age, it was too imperfectly shown in the rock-fragment for accurate determination." APPENDIX B. From Abs. Proc. Geol. Soc. No. 980. Nov. 25th, 1915. p. 6. " Mr. R. Bullen Newton said that he had examined a small series of non-marine Kainozoic remains belonging to recent species, and associated with hard and soft limestones, calcareous sandstones, and conglomerates, which had been collected by the Lecturer, and had determined them as follows : — Ampidlaria ovata (?) Olivier. Locality. — Lak Buna. Distribution. — Recent : Victoria Nyanza, Tanganyika, Nile. Post-Pliocene : Egypt ; Miocene : Victoria Nyanza. Melania tuberculata (Muller) (=curcivosta Deshayes). Localities. — Archer's Post ; Lak Buna ; Chukali Ghofu. Distribution. — Recent : Nile ; Rudolf, Nyasa, Tanganyika, India, etc. Post-Pliocene : Egypt and Sahara. Pliocene : Lake Assal, French Somaliland (formerly regarded as Abyssinia). Miocene : Rudolf (Omo River), Greece, North Italy, etc. Cleopatra bulimoides (Olivier). Localities. — Lak Buna, Chukali Ghofu. Distribution. — Recent; Nile, Rudolf , French Somaliland, Zanzibar. Post-Pliocene : Egypt. Pliocene : French Somaliland. Miocene : Victoria Nyanza. Bythinia and Planorbis spp. Locality. — Wajhir. Limicolaria rectistrigata, E. A. Smith. Locality. — Archer's Post. Distribution. — Recent : Rudolf and Tanganyika regions. Rhacis rhodotaenia, Martens. Locality. — Chukali Ghofu. Distribution. — Recent : Victoria Nyanza and Mount Kenya plateau. Leptospatha spathidiformis (Bourguignat). Localities. — Turbi and Lak Buna. Distribution. — Recent : Rudolf and Zanzibar. Corbicula flumenalis, (Muller) (=saharica, Fischer). Localities.— Turbi, Lak Buna, and Chukali Ghofu. Distribution. — Recent : Rudolf, Marguerite and Abyssinia. Post- Pliocene: Egypt and Sahara. Pliocene : French Somaliland. Miocene: Rudolf (Omo-River beds). Corbicula radiata, (pusilla?), Philippi. Locality. — Chukali Ghofu. Distribution. — Recent : Nile, Rudolf, Victoria Nyanza. Albert Edward, Nyasa, Tanganyika. Post-Pliocene : Egypt. Pliocene: French Somaliland. Miocene: Rudolf (Omo-River beds). * See H. B. Maiife, " The Coastal Series of Sediments in the East Africa Protectorate." Geol. Mag. Juue. 1915. p. 274. 18 COLONIAL REPORTS— MISCELLANEOUS. No vertebrates occurred with these shells, hence their age would probably be younger than the Omo-River deposits north of Lake Rudolf, that had yielded a somewhat similar molluscan fauna, but with the addition of Dinotherium and other vertebrate remains. The presence of that genus, as pointed out by Dr. Haug (Traite de Geologie 1908-11, vol. 2, p. 1727), was indicative of the Pontian or Upper Miocene Period. There are, however, some lacustrine beds near Lake Assal, in French Somaliland (formerly regarded as Abys- sinia), which contain shells also bearing a resemblance to those collected by Mr. Parkinson in British East Africa, especially Melania tuber- culata, Cleopatra bulimoides, Corbicula flumenalis and C. radiata, which are common to both sets of deposits. These Lake Assal beds which are also without vertebrate remains, have been identified by Aubry (Bull. Soc. Geol. France, ser. 3, vol. 14, 1885, pp. 206-209) and Pantanelli (Atti Soc. Toscana Sc, Nat. Proc.-verb, vol. 5, 1887, pp. 204-206, and ibid. vol. 6, 1888, p. 169) as of Pliocene age. i If, from these facts, such widely distant beds can be recognized as contem- poraneous, then the suggestion may be made that the northern half of British East Africa was probably an extensive freshwater region during Pliocene times, linrted on the north by Lake Assal, on the east by Suddidima, on the south by Archer's Post and the Mount Kenya plateau, and on the west by Lakes Rudolf, Stefanie, and Marguerite. Assistance in the determination of these shells had been kindly rendered bv Mr. E. A. Smith, I.S.O." APPENDIX C. Fig. a. 01 Kanjo : Typical gneiss country, looking W. from Archer's Post. b. Part of the W. slope of Marsabit, taken from the summit of a parasitic cone, and showing in the distance others which from their number give a serrated outline to the volcano when seen from far off. c. Puys, arranged linearly, rising from greatly eroded floor of gneiss and schist. Taken from near Laisamis. Gneiss hills in distance. d. Belt of vegetation, marking course of Lak Dera, W. of Afmadu. e. Oxfordian beds of River Juba below Serenti, showing charac- teristic flat tops. The figures appear at the end of the book. EAST AFRICA PROTECTORATE. 19 Note to accompany Geological Sketch- Map of the Northern Frontier District and part of Jubaland, East Africa Protectorate. The degree of accuracy of the map may be partly judged by the fact that the journey, excluding stoppages at Nairobi and Mombi railway journeys and travel in the immediate neighbourhood of the Uganda Railway, occupied between eight and nine months. It is, of course, impossible in so short a time to do more than outline in general terms the coastal plain of alluvium and sediments and the distribution of the lavas on the older crystalline rocks, and it will be understood that the boundaries drawn make no pretence to be more than approximations. It is for instance very doubtful if the volcanic rocks are continuous from the Merti Plateau to Marsabit, and the lava- capped hills east of Langaia and Laisamis are only roughly indicat< d. The numerous volcanoes, in various stages of weathering, the hot springs, fumaroles, etc., south of the Uganda Railway are not shown. In regard to the Jurassic rocks, after they have once been recognized as flat-topped hills rising above the low thorn scrub-covered plain, it is not difficult, from suitable eminences to judge of their occurrence at considerable distances. The but slightly disturbed state of the sediments of the Coastal Belt in Equatorial Africa makes such an inference far less hazardous than it would be in the great majority of countries, and it was though.1 better to show the position of these beds, even in so rough an approxi- mation, than to leave this part of the map a blank. The much younger rocks of Serenli and Eil Wak probably occur locally as outliers on the Jurassic strata. Travel between Serenli and Eil Wak was not allowed. The Koroli Desert is left uncoloured ; it was not visited, but consists, according to available information, of light coloured sands without pebbles. For much information concerning the ground from the S.E. of Lake Rudolf towards Merille, the author is greatly indebted to Major L. 1. At hill, R.A., while other Protectorate officers have most readily placed their knowledge at the disposal of the Survey. This information has been supplemented by the notes often placed on route maps kindly given by the Survey Department of the Pro- tectorate. The latitudes of Eil Wak and Wajhir were fixed by Mr. H. E. Evans. who accompanied the Reconnaissance. March, 1920. John Parkinson. 20 COLONIAL REPORTS— MISCELLANEOUS. NOTE ON THE GNEISSES AND SCHISTS OF THE DISTRICT. A tripartite division of the Gneisses and Schists agrees best with the field evidence. {a) Gneisses of Igneous Origin, (b) Hornblende-Gneisses and Schists, and (c) A Group of Completely Re-constituted Sediments, known as the " Turoka Series."* (a) Gneisses of Igneous Origin. Amongst the old crystalline rocks which form so large a part of the Northern Frontier District is a group of acid gneisses the constituents of which have a granulitic habit, in which microcline is generally conspicuous, and with orthoclase, an acid plagioclase and much quartz together compose almost the entire rock.f Biotite occurs as an accessory mineral, muscovite more rarely. In a thin section the felspars are typically water-clear, and show no signs or but very slight signs of crush. The rocks are of a medium degree of coarseness, the constituent grains being readily visible to the naked eye, i.e., a millemetre or more across ; their colour is pink, greyish or yellowish-white ; commonly they show marked foliation. They thus vary considerably macroscopically, but agree in being non- porphyritic, although they are associated locally with others strongly porphyritic and more clearly igneous in origin. Such rocks are characteristic of many localities ; they form the inlier of fine-grained, well foliated biotite-gneiss about 11 miles N. of Mem (Oringo), the banks of the Uaso Nyiro about 35 miles due E.N.E. of Archer's Post in a direct line.J and appear in many places along the road from the Post to the Kaisut, S. of Marsabit, (Merille, Lai- samis), and at Langaia are associated with thin marbles, i.e., with the Turoka Series. In general character they resemble the fine-grained, well-foliated, non-porphyritic and locally well-banded biotite-gneisses on the northern side of the Fort Hall.§ Granitoid gneisses are conspicuous to the east of Archer's Post associated locally with hornblende-schists. As a rule these rocks are very massive and hard, pink in colour, showing now and again small pegmatite veins and eyes of quartz and are on the whole a monotonous group. The strike of the foliation is *See Quart. Journ. Geol. Soc. 69. 1913. p. 534. fFor a similar assemblage see A. Holmes on the biotite-gneisses and gneissose granites of Mozambique. Quart. Jour. Geol. Soc. 74. 1918. 1 1. r>2. Predominance of microcline and occasionally granulitic texture characterize the Basement Gneisses of Benguella. See G. W. Tyrrell. Trans. Roy. Soc. Edin. 51. 1916. p. 538. J Rocks from here closely resemble the flaggy gneisses of the Turoka basin near the Magadi Railway and the biotite-gneisses of II Bisil to the south. Sec British Museum slides. Nos. 1913, 397-5 and 15. § Brief reference is made to t lie Fort Hall rocks by Maufe, see Col Rep. Miscell. 1908. Cd. 3828. p. 22. EAST AFEICA PROTECTORATE. 21 generally N.N.E. Elsewhere, also in the eastern part of the Northern Frontier District, between Ajow and Debell, well-marked ridges oi similar massive pink gneiss, having a strong foliation trend X. and S. As a sub-division of the foregoing we may separate, tem- porarily at least, the more clearly igneous gneisses of the Uaso Xyiro, E. and W. of Archer's Post, at Chanler's Falls and in the neighbourhood of Moyale. Brief reference to this type of ortho-gneiss will suffice. Westwards of Moyale, the great ridge which culminates in Burroli, consists of massive pink granitoid gneisses, occasionally poor in quartz, although elsewhere the amount is rather above the average for the type. Peg- matites containing crystals of flesh-coloured felspar, dykes of con- sanguineous origin and evidences of fluxion are common. At Mangatt, near Moyale, hornblende-schists, occasionally garnetiferous are not rare and are associated with numerous pegmatite dykes, which cut across the foliation (N.N.W.-S.S.E.) or occur as sills. Excellent exposures are found showing a hornblende-bearing rock brecciated by one more acid and forming a coarse banded gneiss in the usual way. Similar characteristics are shown by the gneiss at Chanler's Falls, especially at the lower rapids. Passing from the extreme north to the extreme south of the Northern Frontier District, such rocks are found along the Uaso Nyiro, W. of Archer's Post, usually massive, streaky, granitoid and banded gneisses crossed with pegmatite veins (W. of Koitorgor and above the rapids W. of the Ngare Ndare). The more basic part contains both hornblende and mica. Petrology. The normal type of the basement gneiss is represented to the N. of Langaia and at Merille by granulitic gneisses of acid composition ; compact light-coloured rocks of medjum grain, not showing very conspicuous foliation and speckled with flakes of black mica. With the exception of a few grains of epidote and zircon this brown mica is the only coloured constituent and in the Langaia example some magnetite and abundant muscovite. In this rock microchne is the most conspicuous mineral betweeu crossed nicols, while in that from Merille a noticeable amount of soda lirne felspar occurs varying from oligoclase to oligoclase-andesine, the former the more common and associated with some microcline and orthoclase. In both rocks the quartz forms crystals with rounded and lobed cross sections, the lobes sometimes lengthening into apophyses, and appears to have embayed and corroded the felspars. In the Langaia rock there is a tendency to form vermicular quartz. The slabby gneiss of Laisamis, a short distance to the north, contains occasionally a few small garnets, conspicuous microperthite (in a thin section), an acid plagioclase and some microcline A specimen labelled descriptively from superficial appearance " Bed " in gneiss collected south of Laisamis is of interest as showing dominant scapolite in a thin section. By the aggregation of yellowish- green epidote associated with green hornblende, or. large elongated grains of quartz with some epidote, the former generally slightly crushed, the rock shows a tendency to be banded. Sphene is not rare and apatite occurs. A few small grains of calcite were noticed, usually associated irregularly with hornblende. Felspar, apparently oligoclase is very rare. 22 COLONIAL REPORTS— MISCELLANEOUS. Of the less normal members of the series, a specimen collected from near Langaia, in which the dark minerals are rather irregularly or cloudily distributed, contains a considerable amount of microcline which bears a very similar relation to the quartz as in the slides first mentioned, bul which differs widely in containing garnet, magnetite, sphene and apatite as important constituents. Zircon and epidote are accessory minerals, a thin edging of the latter in some cases sur- rounds the garnet but without forming a distinct graphic structure. The garnet is yellowish-green by transmitted light and forms irregular brownish-black blebs in the hand specimen. An associated lock of close texture, dark greyish-green in colour faintly mottled with red, found between Merifle and Langaia, contains a large amount of almost colourless epidote together with sphene and a brownish-red garnet, which is rarely even partially idiomorphic but shows irregular amoeboid sections. Together, the garnet, epidote, and sphene, which may build sponge-like crystals of considerable size (1*5 mm. in diameter) App. D. Fig. b, form rather more than one half the slide, the remainder consisting of plagioclase usually faintly twinned or not at all, but with a refractive index considerably higher than balsam and belonging accordingly to the basic end of the series. Microcline is absent in this slide. Apatite is an accessory mineral. This and the sphene preceded the other minerals in consolidation; the epidote was slightly earlier than the garnet. In a somewhat similar rock from the same locality, in which green masses of epidote are the distinctive feature, the felspar is again difficult to determine, the majority of the crystals have a refractive index greater than that of quartz, while in others a lower figure indicates a more acid variety. The dominant epidote forms irregular polygonal crystals in bands which contain no other mineral except a few grains of sphene and rarely zircon, but occasionally open out round nests of felspar. Microcline is absent- Collected from the main track about one mile S. of the camping ground known as Misa, some 12 miles from Moyale on the Abyssinian frontier, is a dark rock of close texture consisting of very pale pink garnets (in a thin section) and light browm hornblende in approximately equal proportions. The pleochroism of the latter is, A & B pale straw. C, Yellowish- brown. In addition to these constituents some quantity of a pyroxene, in texture and colour closely resembling the garnet, may be the origin of part of the hornblende, but the inclusion of crystals of the latter in the former, having different orientation and no passage zone shows the hornblende to be for the greater part a primary mineral. Unlike the garnet-epidote-gneiss already described, the garnet of this rock has a distinct tendency towards idiomorphism when opposed to the felspar although the crystals are never perfect and occasionally almost cir- cular in section. Occupying interspaces between the other minerals is a translucent laboradorite, making about one-tenth of the whole. In this connection a grey and white rather coarse gneissose rock from the hill immediately behind Archer's Post is of interest. In a thin section it is seen to contain microcline, an untwinned felspar probably orthoclase in lesser quantity, quartz, epidote, and malacolite, the fourth and fifth minerals with sphene constituting about half the rock'. Grains of dolomite which have the appearence of being original. EAST AFRICA PROTECTORATE. 23 are rather common. The pyroxene is largely altered into green horn- blende. Apatite and zircon are rare. The occurrence of epidote, garnet, hornblende, and sphene and occasionally carbonates, with locally sea polite in rocks which appear to be integral parts of the gneiss series is of especial interest, and recalls the mineral assemblage due to the alterations of limestones by granite- gneiss bathyliths such as are described by Adams and Barlow.* The presence of marble at Langaia, where these abnormal rocks occur is significant. In the Canadian district the evidence is far clearer than will probably ever be the case in British East Africa, but in the writer's opinion the suggestion is worthy of consideration that the acid gneisses here described are intrusive into a series of sediments, now completely crystalline schists, i.e. the Turoka series. A paper by Dr. A. Holmesf on the " Pre-Cambrian and Associated Bocks of the District of Mozambique " supports this view as to the relative ages of the crystalline schists and the granitic magma in that district, as does a recent paper on Southern Rhodesia by Mr. Brantwood Maufe. J Dr. Holmes thinks it possible that the hornblende-gneisses, amphibolites and garnetiferous rocks of this part of Mozambique might have been formed by the intrusive granitic magma when limestones or dolomites were encountered, that the argillaceous element in the ori- ginal sedimentary series became granitized, and that accordingly " the gneisses may be interpreted as composite rocks in which, as a rule, the granitic element predominates." (p. 66.) A noteworthy point of difference between the Mozambique area and the Northern Frontier District is that in the latter no passage between the gneisses and " indubitable granites " was observed. Speaking of the Metamorphic System of Southern Rhodesia, con- sisting of schistose rocks and granite bathyliths, which "as a whole appear to be continuous across the §Limpopo River with the Swaziland System of the Transvaal," Maufe remarks that " the general simi- arity " of the rocks and the Archaean System of Canada has been already pointed out by other Geologists. This explanation of the Canadian Archaean structure implying " the upwelling of molten granite " accompanied by the " sagging of the overlying rocks into intervening troughs " '* accounts for the coincidence between the strike of the schists and banding of the gneisses " of Rhodesia upon which Maufe briefly dwells, and the characteristic structure of the intrusive series, a " flow-banding due to movements taking place during crystallization," typically developed about the margins of the bathyliths. The fine-grained gneisses 35 miles E.N.E. of the Post in a direct line call for little comment. * " Geolo^v of the Haliburton and Bancroft Areas, Province of Ontario." Depart, of Mines. Geol. Survey. Mem. No. 6. 1910. p. ST. f Quart. Jour. Geol. Soc. 74. 1918. p. 31. Also Abstract. Geol. Mag. for August 1917. p. 380. ;'[ Southern Rhodesia. Geol. Surv. Bull. No. 2. " The Association of Gold Deposits with Acid Igneous Rocks in Southern Rhodesia."' Bulawayo, 1913. § op. cit. p. 4. 24 COLONIAL REPORTS — MISCELLANEOUS. In micro-structure they closely resemble the Oringo inlier next mentioned. A mica, green in a thin section with strong absorption, magnetite, sphene, apatite, and rarely ilmenite are accessory minerals in rocks characterized by microcline, oligoclase and the irregular almost globular habit of the quartz. The Oringo Inlier. The Oringo inlier, 11 miles N. of Meru, is a fine-grained well foliated biotite-gneiss containing 25-33 per cent. of microcline and subordinate oligoclase. It is not porphyritic. A few flakes of greenish-brown mica represent the ferro-magnesian minerals, and quartz is the most conspicuous constituent forming grains with lobed or undulating cross sections suggesting corrosion of the felspars. The mineral shows slight evidences of pressure. Round blebs of quartz included in the felspar and a tendency to form vermicu- lar quartz are characteristic of the rock. The gneisses from the northern side of Fort Hall are essentially the same, though rather coarser than the rocks previously -described ; a few small and shapeless grains of garnet in one slide are noteworthy, as is locally the large number of inclusions contained in the quartz. Darker bands in this rock arise through increases in the content of the mica, or by the incoming of hornblende associated with sphene and much apatite. In the slides examined, no microcline was noticed, the mineral most typical of the acid associates. It may be remarked in passing that between the Thika and Fort Hall the old crystalline rocks come into view in the descent to the Maragun River, finely banded mica-schists or gneisses predominating, associated with hornblende- schists and rarely pegmatites. On the northern side of the Station the fine-grained, non-porphyritic biotite-gneisses now mentioned predominate, occasionally well-banded. Here pegmatites are common and in some instances become massive and appear to pass into the finer gneisses. (b) Hornblende-Gneisses and Schists. The polymorphic origin of the amphibolites demonstrated by Adams and Barlow for the Haliburton and Bancroft area may obtain in East Africa but much more work would be required before this could be asserted.* Of these rocks, that from the southern side of the hill on which ' Archer's Post stands, is of fine grain and rich in apatite and magnetite, probably also ilmenite. The green hornblende forms irregular grains, about "25 mm. long, and shows the usual pleochroism from dark sage-green to greenish-yellow. It forms about half the rock. Quartz locally predominates over the oligoclase-andesine,i but the felspar is often untwinned and commonly shows an attempt at zonal structure. Small and shapeless garnets occur but are not common. Peculiar ovoid patches, 1-|— 2 mm. long, conspicuous in the hand specimen, consist of groups of irregular or polygonal felspar grains, flecked with iron oxide and apatite. Presumably these represent the breaking- down and re-crystallization of the phenocrysts of the original rock. * op. cit. p. 157. EAST AFRICA PROTECTORATE. 25 A second example from the same hill, where it is associated with fine biotite-gneisses contains a higher percentage of the specific mineral, and strings of granular sphene. This mineral and (probably) ilmenite, the latter not unfrequently enclosed in the former, are both earlier than the hornblende. As before the felspars are zoned and rarely show twinning, some, probably most, are an acid plagioclase. Related to these is a hornblende-epidote-schist from Koitorgor, Z\ miles W. of Archer's Post where it is associated with a variety of types. A coarse gneissose pegmatite with conspicuous phenocrysts of microcline and marked foliation forms the top of the hill.* Marble was found as boulders on the slopes, but not in situ, indicating the presence of the Turoka Series, as possibly does a schist containing quartz, epidote, and hornblende. The specific mineral of the hornblende-schist is sometimes derived from malacolite. Magnetite (?) and sphene have preceded the epidote in consolidation. The felspars are of more than one species, the majority show no decided twinning and have a refractive index very near to that of quartz, twinned crystals are a rather basic andesine. Hornblende-schists are conspicuously developed 7 or 8 miles S. of Laisamis on the main caravan route from the Post to Marsabit, where they are associated with acid gneisses. The former not unfrequently show augen structure and are doubtless of igneous origin. An interesting rock from this neighbourhood consists of pale green hornblende, through which are scattered grains of non-ichomorphic dark green pleonaste or hercynite. App. D, Fig. a. Interspersed through the amphibole are nests of translucent anorthite or labradorite, seldom showing twinning, and forming about 25 per cent, of the whole. The pleochroism of the hornblende is, A and B very pale straw, C pale grass-green. The pinacoids are rarely, if ever, developed. Mag- netite is absent in this slide. Hornblende-schists are also common on the S. edge of the Kaisut, not far S. of Marsabit, where they are associated with slabby, felspathic gneisses. Resembling the Koitorgor rock, inasmuch as it contains ragged plates of an almost colourless pyroxene, is a hornblende-schist inter- calated in the quartzites of Ajow. There is, however, no epidote and the hornblende is apparently of primary origin. The colourless constituents which form about | the slide, are a preponderating acid labradorite and quartz. (c) The Turoka Series. Typical rocks of this Series of altered sediments are excellently exposed near the eastern border of the Northern Frontier District, at Ajow and Buttellu.| The quartzites of Ajow so closely resemble in their peculiarities those near the headwaters of the Turoka River that it is impossible to doubt that they belong to one and the same group of beds. Obscurity of bedding planes and a general massive habit are characteristic The rock is almost pure quartz, though magnetite may be a noteworthy accessory in addition to small flakes of a green * For what it is worth, this goes to show the gneiss is later than the crystalline schist group. t See references to what are probably members of this Series. Maufe, Col. Rep. Miscell. Cd. 3828. 1908. p. 19, 20. 26 COLONIAL REPORTS -MISCELLANEOUS. and white mica and of tourmaline. The state of crystallization of the Ajow and Turoka Biver quartzites is identical with that of the rocks described by Prof. Gregory from Benguella,* the Bailundo Schistose Quartzites, a group which he correlates with the Kafubu Quartzites of the Congo and the Swazi Series of South Africa. In East Africa, the Turoka Quartzites in the typical exposures are not schistose. Near Buttellu, excellent exposures of the various members of the Turoka Series appear, consisting principally of marbles interbedded with quartz-schists, many of which show signs of crush. The former rocks are free from lime-magnesian silicates and none seen were so coarse as those in the neighbourhood of the Turoka River ; the latter occasion- ally contain some quantity of mica either occurring as lenses or distributed through the rock. The strikes of the foliation planes are from 315° to 330°, the dips about 40° to 45° to the S.W. They thus differ from the usual approxi- mate N. and S. strike of the gneiss to the W. and S.W. Above the wells, banded marbles are conspicuous, the variations being largely due to alterations of texture rather than to the intro- duction of silicates. Evidences of crush are obvious and are excel- lently seen in thin sections. A few bands of biotite-gneiss are associated with the marbles. The quartzite of Ajow consists of large grains of quartz, up to 10 mm. across, having irregular or dove- tailing edges, giving no indication of a clastic origin, and showing little or no signs of crush. Near the Ajow wells a fine-grained, grey, banded micaceous gneiss, associated with a pegmatite, is interbedded with the quartzite. These gneisses are relatively insignificant, but it is noteworthy that the massive quartzites. of the Turoka River are interstratined with important gneisses of similar type. How far some of the uniform gneisses in the Northern Frontier District should be placed, as a somewhat arenaceous part, in the Turoka Series must remain doubtful until additional work is done.| Other rocks which form part of the sequence at Buttellu deserve brief notice. One bed, itself well banded, about 6 feet thick, is composed of dusty quartz, large grains of pink garnet and reddish-brown mica — the latter frequently included in the former — and is clearly related to * Trans. Roy. Soc. Edin. 51. 1916. p. 527. Pt. 2. fig. 4. Compare also Dr. Holmes .n ih: pap.-r to which i\ 1'. n lie ■ has already l>een made, and P. A. Wagner. "The Greolo ral Industry of South-West Africa," Union of South Africa. Geol. Surv. Mem. No. 3. L916. p. 40. Ball and Shaler (Econ. Geol. 9. 1914. p. 662) mention that " Graphitic metamorphosed sedimentary rocks, supposedly of pre-Cambrian occur abundantly in the Manyiema-Kivu region." Note also Andrews and Bailey (Quart. Jour.' Geol. Soc, 66. 1910. p. 189) on "a very distinctive group of rocks from the eastern portions of Central Angonaland. "Graphitic gneiss > rbanded with fine-grained fels- pathic gn iss, thick beds of crystalline Limestone and kyanite-schists," are m< q1 on d (p. 194). Allied sediments occur in the Nyika, N.W. i nd ot Nyasa and s. of Fort Maiming. " Graphitic gneisses and limestones can be trac d southwards for a considerable distance down the Shire Valley." The Series "is again met with in the Port Herald district." p. 19!. t Such for example as the gneisses 35-37 miles due E.N.E. of Archer's • Post. EAST AFRICA PROTECTORATE. 27 the kinzigites. In the hand specimen the garnet and mica form a band 15 cm. thick. Small crystals of microcline are intercalated between the much 'larger grains of quartz in vein- like aggregates, but in quantity are of very secondary importance. Signs of crush are again evident. Closely associated with this rock is one coarse in texture and strongly foliated, in which quartz is rare or absent, which contains large crystals of brownish-red garnet, occasionally 10 mm. long, mica and sillimanite. The last two minerals, closely mingled, the sillimanite forming a dense felt, constitute the greater part of the thin section. The garnet, distinctly pink in the hand specimen, colourless and latticed with cracks in a thin section, tends to segregate into bands of peculiarly solid appearance. Microcline and possibly another felspar form locally a kind of base in which the remaining minerals are set, but the quantity is small. The rock apparently underlying these, presents some points of interest. It is a rather coarse quartz-schist or quartzite containing infrequent crystals of translucent felspar, sometimes apparently microcline, a few amoeboid granules of pink garnet, flakes of the characteristic reddish-brown mica and rarely muscovite. A slabby structure is well developed and felts of small sillimanite needles have fcrmed between the cracks of the quartz grains. The latter are full of . inclusions and show marked undulose extinction. The rock overlying the garnetiferous gneiss is essentially similar in the hand specimen dull, iron-grey, necked with small white lenticles. It con- tains much more sillimanite and brown mica than the preceding, arranged with strong foliation in broad bands ; the remainder of the rock consisting of crushed quartz and grains of translucent felspar, the latter distinguished by fine irregular twinning and undulose ex- tinction, and having a refractive index less than that of balsam. A rock of interest occurs rather high up in the Lak section at Buttellu. In the hand specimen it is a slabby micaceous gneiss, grey-brown- in colour, rather granular and of close texture, the abundant flakes of brown mica being just visible to the naked eye, and distinguished by numerous white almond-shaped lenticles, producing the appearance of a greatly crushed and highly altered conglomerate. These lenticles reach 20 mm. in length by 2\ mm. in breadth and are spaced so that three or four occur on a surface 6x2 cm. measured •at right angles to the foliation. In a thin section flakes of a yellow- brown mica, locally folded and faulted, elsewhere forming films between the other constituents independently of the direction of foliation, grains of translucent felspar and some quartz are seen to constitute the " matrix " of the rock. The grains of felspar show very irregular twinning and extinction, due largely no doubt to crush. Occasionally the mineral is zoned. The refractive index is less than that of balsam, but possibly several varieties are present. The lenticles consist of felted masses of sillimanite ; smaller groups of crystals continue along the same plane of foliation, but may be replaced by greatly broken garnet, the interstices between the fragments being filled with brown mica. It is inferred that the rock is of sedimentary origin and that the sillimanite lenticles represent pellets or streaks of more nearly pure day than the remainder of the rock. 28 COLONIAL REPORTS -MISCELLANEOUS. Evidences of crush in a few of these rocks are very obvious, some thin sections recalling mylonite. Belonging doubtless to the same series, although not found in situ, is a peculiar rock common as fragments about 3milesN.E. of Buttellu wells. It consists of three minerals which are in order of quantity quartz, magnetite, and augite, the first named constituting nearly half the slide. The pyroxene is considerably altered, and is yellowish- white or reddish-brown by reflected light. The magnetite and augite form very irregular crystals interlocking with the quartz. The marbles collected present few points of interest, and only two have been sliced, one from Buttellu, the other from the plateau N. and W. of Olloromade in the S.W. corner of the Northern Frontier District. The latter contains graphite and flakes of white mica. Macroscopi- cally, the rocks are usually homogeneous in appearance and coarsely crystalline, individual grains measuring 3-4 mm. across being common. Small pebbles of graphite-gneiss occur in the bed of the Uaso Nyiro below Olloromade, the specific mineral constituting half to one-third of the rock. It was not found in situ. Intrusive Bocks. Of the earlier intrusive rocks, a boss 5 miles X. of Ajow is a granite of medium grain, showing locally gneissose structure. Microcline, microperthite, often in coarse intergrowth are characteristic, the crystals separated and traversed by narrow zones of granularized material. A little yellowish-brown mica is the only ferro-magnesian mineral. The rock is obviously of considerable age. The granite from the old road at Moyale (Abyssinian Frontier), although not unlike that of Ajow in a hand specimen shows in a thin section more biotite of a reddish-brown colour, an absence of microcline and perthitic intergrowths and less conspicuous signs of crush. Ortho- clase and some acid plagioclase, greatly altered, form about half the rock, the bulk of the other being quartz comparatively free from inclusions. An important mass of fresh-looking olivine-gabbro is intrusive into the quartzose schists and granitoid gneiss, which elsewhere form the northern bank of the Uaso Nyiro, about 15 miles W. of Chanler's Falls. The 'exposure is about 6 miles long. The olivine shows some serpentinization and the separation of iron oxides along cracks. The diallage is frequently changed peripherally into a yellow- ish-green hornblende and both minerals are occasionally edged by a border of pale green radiating actinolite. The felspar is at least in part a labradorite. A serpentine was found at Debell and again at Misa, 15 miles to the N., and S.E. of Moyale. At the former locality the serpentine is associated with a talc-schist, which may prove to be the result of crushing of the former rock. Indications of a possibly older series of basic intrusives, between the water-hole at Olloromade and the Uaso Nyiro, were found in boulders of a far from fresh-looking spheroidal basalt enclosing fragments of the gneiss. This may be an offshoot of a greatly altered oli vine-free ophitic gabbro found as a pebble at Olloromade camping-ground. My thanks are due to Dr. G. T. Prior and Capt. W. Campbell Smith, M.C., for placing the collection of African rocks in the British Museum at my disposal. March, 1920. John Parkinson. APPENDIX C. J?2*~ Fig. a. Fis. b. APPENDIX C APPENDIX C. Pier. d. Fiff- e. COLONIAL REPORTS- -MISCELLANEOUS. 29 APPENDIX D. Fig. a. Amphibolite with spinel. 7-8 miles S. of Laisamis. x 35. Fig. b. A single crystal of sphene with garnet and epidote in gneise Between Merille and Langaia. X 35. These photomicrographs were kindly taken by Mr. J. A. Bull- brook, F.G.S. APPENDIX D. fe% ^4k Vl/1* $8 m / Hornhlena^^^m Fig. a. Pig. />. 10 O ifnbnqui9~y J/3L/S apeuiajQ/iQ Hied njgyy -uaAft tjnjnujnu djes§ eidi>fie~i ,e /°S 7 LL sbuey jjepjjou lesonoqiQ '••" 7J r e /V 7 fSOJ s^si/^jp \ // 1/0/3399 7 uoij3»s iinjnwny 6000 ft Lo I Inch 3 ■=, I3-" n d J° SJap/noff I I hr: • i 1 1 1 r-t: fffifflff wS 3 o CD < W Q < H cn < h (0 o 0.