158 de. r. Oswald ox the [June 19 14,. 



a landmark, this travertine is more fully exposed over a wider area. 

 Here the succession consists of : — 



Thickness in feet inches. 



(1) Greenish-grey sandstone, with bones of baboon. 2 to 6 



(2) Grey gravelly clay, with streaks of sand and 



gravel 3 



(3) White calcareous travertine, with bones of 



Elephas aff. meridionalis. Hippopotamus, 

 Phacochcerns, and antelope l 6 ins. to 1 6 



(4) (Base not seen.) Greenish-grey clay 4 



The beds have been thrown into a broad syncline ; for, in the 

 western part of the exposure, they dip 20° south-south-eastwards, 

 and in the eastern part (about 150 yards distant) they dip 50 J 

 north-north-westwards. These directions differ altogether from 

 those observed in the sandstone cliff 5 miles away to the east, 

 but it is probable that they are due to a local subsidence, perhaps 

 caused by the leaching-out of underlying soda -beds, for there is 

 still a strong efflorescence of soda on the surface of the beds of 

 clay, and the crust is continually collected by the natives, as at 

 Lake Simbi. 



These beds are probably of late-Pliocene age, and they may 

 be compared with the beds found north of Lake Rudolf, in the 

 lower course of the Omo River, by E. Brumpt 3 in 1903, containing, 

 among other bones, ILipparion (near to the Pliocene H. lybicum), 

 Hippopotamus, Rhinoceros, Phacochoerus, Bvjf'elus, Camelopar- 

 dalis, antelopes, and Elephas cf. meridionalis. A tooth of 

 Dinotherium was also recorded from these beds ; but, either it is 

 a Pliocene species, or it may have been derived from some earlier 

 beds similar to the Karungu Miocene Series. The uppermost 

 stratum consisted here of gypsum, and I have already suggested 

 that the gypsum beds of the south-eastern angle of Homa Bay 

 probably belong to the Pliocene Series north of Homa Mountain. 



A rounded spur of horn blende-biotite- gneiss rises out 

 of the low-lying country east of Lake Simbi, and this granitic 

 gneiss, 3 which shows a more marked cataclastic structure than any 



1 These fossils will shortly be described by Dr. C. W. Andrews in a future 

 paper. 



2 E. Haug, ' Traite de Geologie ' vol. ii, pt. 3 (1911) p. 1727. 



3 The rock contains abundant allotriomorphs (up to 8 mm.) of plag-ioclase 

 (oligoclase-andesine, Ab-An 3 ), in which the fine twinning is often re- 

 peatedly bent ; only traces of zoning are present, and decomposition-products 

 (white mica, calcite, epidote, and zoisite) occur centrally. Orthoclase is less 

 in quantity and in smaller grains (up to 4 mm.), usually turbid centrally. 

 Green hornblende (up to 3 mm.) is fairly abundant (a, pale straw ; /J, olive- 

 green ; y, blue-green), sometimes twinned, occasionally bent; it is especially 

 associated with quartz and some may have recrystalbized ; occasionally with 

 epidote and calcite centrally. Biotite is rather sparing, and has altered 

 either to chlorite or to a mixture of chlorite, epidote, and zoisite ; it has been 

 much crinkled and contorted, encloses apatite, and is associated with magnetite 

 and sphene. Magnetite occurs in a few crushed grains, and several 

 pinkish-brown crystals of sphene are present. Quartz is abundant, very 

 much crushed and rolled out into lenticular masses ; the grains show denti- 

 culate margins and undulose extinction, with strings of inclusions. 



