THE VICTORIA NYANZA 
3 
Kachuku and at the base of the basalt cliffs of East Kachuku 
and Kikongo. 
Broadly speaking, these Miocene sediments, brought 
down by a large river and deposited in the lake, may be 
classified into three groups, which I divided into 37 
beds : — 
1. An Upper Series (Beds 1-12), about 70 feet thick, of 
grey and brown clays and shales, with occasional beds of grey 
sandstone and thin seams of travertine. 
2. A Middle Series (Beds 13-25), about 30 feet thick, of 
variable red and grey clays with white sandstones in the 
lower half. 
3. A Lower Series (Beds 26-37), about 35 feet thick, of 
buff sandstones, calcareous conglomerates, and torrential 
gravels (containing the Dinotherium zone), passing down into 
clays and marlstones. 
Travertinous beds occur at frequent intervals throughout 
the whole succession of strata, which do not exhibit any 
unconformity. 
At Nira the Miocene beds rest on an uneven floor of a 
fine-grained amphibolite (hornblende-rock) belonging to the 
ancient gneisses and schists which are so widely distributed 
on the eastern and southern coasts of the Victoria Nyanza. 
At Kachuku, however, the lowest beds lie on a quartz-ironstone 
breccia which faces the Kuja plain in a low cliff. Probably 
this breccia of angular fragments of quartz embedded in 
limonite represents the weathered detritus of old amphibolites 
or hornblende-schists composing the original land-surface 
which was invaded by the advancing waters of the lake in 
Lower Miocene times. 
The initial depression of the land must have taken place 
with relative rapidity, for the lowest bed (No. 37) is not a 
gravel or a sandstone but a fine clay, indicating that it was 
deposited in fairly deep water at a considerable distance from 
land. This mottled crimson and yellow clay becomes wholly 
red in colour in the proximity of a quartz- vein, which has not 
only traversed the underlying platform of hornblende-rock, 
but has even forced its way into this red clay ; and the red 
colour, penetrating every crack and joint of the clay, is probably 
