136 de. f. Oswald on the [June 191 4, 



portion has been uncovered. The occurrence of stone-implements 

 of a Neolithic character (chiefly made of de vitrified obsidian, but 

 also of quartzite and quartz-porphyry, all with a thick brown 

 patina), which I found lying on the wide terraces of Beds 23 & 26, 

 both at Nira and at Kachuku, seems to indicate that a considerable 

 space of time has elapsed since the first formation of these gullies. 

 Every year will see a larger area exposed by the torrents of the 

 rainy season, and a periodical search by a geologist or by a Grovern- 

 ment official on his round of the province through Karungu would 

 certainly result in important finds. 



Everywhere I found the dip of these beds constant : namely, 

 8° north by west. As a result of this northerly dip, they soon 

 disappear completely beneath the basalt-plateau, which extends for 

 30 miles northwards ; and even the deep meridional valleys at 

 Kitama and Kikongo failed to reveal any trace of them. These 

 broad valleys seem to have been excavated in the deposits prior to 

 the eruptions of the basalt, which flowed down into the valleys 

 from the higher ground, completely covering and sealing up the 

 lateral slopes. Another reason for believing that a great part of 

 these deposits must have been destroyed by denudation before the 

 outflow of the lava-streams, is founded on the circumstance that 

 the continuity of the beds between Nira and Kachuku has been 

 interrupted by a basalt-flow extending from Nira Hill down to the 

 actual level of the plain, filling up an old valley which had been 

 eroded in the soft clays and sandstones. 



Even on the south, no traces of the beds could be discovered. 

 In this direction the uplifted strata, which also thin out south- 

 wards, would have occurred at a continuously higher level, and 

 were therefore more liable to be destroyed by denudation when the 

 lake stood much higher than at present, or by the erosion of the 

 Kuja and its tributaries. 



South of the wide Kuja Valley I could find no indication of 

 them in the hills of granitic gneiss, which extend to the Anglo- 

 G-erman frontier — despite the fact that this area is probably a 

 depressed block of land, judging from the obviously drowned valleys 

 lying between the long narrow promontories of Mohuru ; but the 

 initial formation of these valleys may have preceded the deposition 

 of the Miocene sediments. 



The shallowness of the Bay of Karungu, in sharp contrast with 

 the steep gradients of the lake-bottom along the coast to the 

 north and south, indicates that the Miocene deposits had once a 

 considerable westward extension over the site of the bay, and have 

 been destroyed by the action of the waves, which break on this 

 shore in heavy rollers. =u 



There are, indeed, indications that the series thins out southwards, 

 and probably it never extended very far in that direction. The 

 exposures, both at East Kachuku and at Kikongo, lie considerably 

 (namely, 6 furlongs and 10 furlongs respectively) to the south of 

 the line of strike of the outcrops at Nira and Kachuku, and in both 

 the two first-named localities the lower beds have thinned out 



