THE GEOLOGICAL COLLECTION. 425 
cover so large a proportion of British East Africa. In the area 
where this series is most developed, the lavas are of many different 
types, only one of which is represented in Dr. Donaldson Smith's 
collection. 
This is the trachytoid phonolite, which is one of the most re- 
markable rocks in the series. Dr. Smith collected fragments in 
Marsabit and the Omo valley, and thus extends the range of this 
rock a considerable distance to the north, and helps to link the 
lavas of Laikipia with those of Abyssinia. 
The only fossil from the Cainozoic alluvial deposits on the floor 
of the Omo valley is too broken to be identified. Mr. E. A. 
Smith has kindly examined it with much care, and reports that 
it is probably a specimen of .4¢theria; but even its generic posi- 
tion cannot be determined with certainty. This is unfortunate, as 
mollusca from these alluvial deposits of the Rift Valley are among 
the greatest desiderata in East African geology. If future travellers 
would do their best to collect such specimens, geologists would be 
erateful to them. 
Dr. Donaldson Smith’s collection is therefore of interest, as it 
gives us a fair idea as to the distance to which the rocks of British 
East Africa extend to the north. 
