Yol. 70.] MIOCENE OF THE YICTOBIA ITTAJfZA, ETC. 143 



calcareous concretions or kunkar are frequent, while in the wide 

 valley of Wawengi (between Karungu and Omangi) bones of ante- 

 lope, zebra, warthog, etc., sometimes occur : probably the animals 

 were mired in the extremely sticky black clay during the rainy 

 season. 



The presence of this regur with land-shells over the zone of 

 Miocene beds along the foot of the lava -streams, and the absence 

 of any freshwater shells, would seem to indicate that this area has 

 not been submerged by the lake since the uptilted Miocene deposits 

 were concealed by lava. In the gully of West Kachuku, however, 

 the lower half of the regur showed a roughly- stratified layer of 

 boulders of basalt with fragments of the Miocene sandstones, and 

 these were probably brought down by a temporary torrent during 

 an exceptionally heavy rainfall. 



Inland the impervious substratum necessary for the formation of 

 the regur is provided by a yellow loam ; for instance, in the 

 Kitama Valley, 4 feet of regur overlay 6 feet of yellow-brown 

 loam (derived from the disintegration of the basalt), containing 

 small lumps of kunkar and land- shells, together with occasional 

 -angular fragments of basalt (about 2 inches in diameter), and 

 weathering in vertical walls, the whole presenting great similarity 

 in appearance to the loess of China. Similar relations between the 

 regur and the loess occur also in the wide vallevs draininsr into 

 Karungu Bav. 



It was exclusively in the basaltic region that I observed this 

 black earth, both in the Karungu district and again over the 

 Rungwena Plateau (south of Homa Bay) nearly as far as Langueh. 

 In the banks of the Agulu Muk River, which cuts through this 

 plateau, I noticed the following succession : — 



Tli ickness in feet. 



(1) Regur 4 



(2) Compact, calcareous, brownish - grey loam (loess), with 



fragments of basalt 3 



(3) Soft grey clay, with fragments of basalt 4 



(4) Coarse yellow gravel, with partly rounded blocks (mea- 



suring as much as 18 inches in longest diameter) 

 of quartz-porphyry, quartzite, andesites. and banded 

 jasper, dipping 5° north-eastwards, that is, toAvards 

 the river 3 



(5) Quartz -porphyry in situ, much decomposed. 



As one descends to the lake from the Rungwena Plateau, the 

 following section is seen in the right bank of the Rungwena 

 River : — 



Th ickness in feet. 



(1) Regur 3 



(2) Hard grey volcanic tuff, dipping 8° north-north-west- 



wards, that is, towards the river 1 



(3) Brown clay, with sparse pebbles of quartzite. granite, 



basalt, jasper, and ironstone 4 



Nearer still to Homa Bay, Seminya and the hill west of it 

 consist of a grey volcanic tuff, dipping 2° northwards, veined with 

 haematite. Probably Ruri was the centre of the explosive action 

 Avhich gave rise to these tuffs. 



