424 APPENDIX E. 
small exposures of later Paleozoic and Mesozoic deposits; 3. A 
series of volcanic rocks of various dates, but all post-Jurassic; and 
4. Sundry alluvial deposits of Cainozoic age. 
Dr. Donaldson Smith’s collection includes representatives of the 
Ist, 3d, and 4th of these divisions. 
The Archean rocks are the oldest, and form a plateau, upon the 
eroded surface and flanks of which the other rocks were depos- 
ited. The Archean series was known to occur in Somaliland 
south of Berbera and Zeila, and in Abyssinia; and also to form a 
band across British and German East Africa, and southward thence 
as far as the Transvaal. The most northern points at which they 
have previously been found is in the Loroghi Mountains, where 
they were collected by Lt. von Hohnel; so that the specimens 
found by Dr. Donaldson Smith help to connect the Somali 
gneisses with the typical East African series. The specimens col- 
lected are much altered, and stained green by secondary epidote ; 
but similar rocks have been found by Mrs. Lort Phillips in Somali- 
land,’ so that there need be no doubt as to the correctness of their 
identification as members of the Archean. 
The Permocarboniferous rocks of the Sabaki valley are not rep- 
resented in the collection, but there are many fragments of Jurassic 
ammonites from Somaliland. Baron von der Decken during his 
fatal ascent of the Juba in 1865 noticed specimens of limestones on 
the right bank of the river. It seems probable that these were 
part of a band which once extended from the Jurassics of Mombasa 
and German East Africa to those of Abyssinia. Dr. Donaldson 
Smith has collected a single brachiopod which gives a more sat- 
isfactory basis for this hypothesis. It is identified by Mr. F. A. 
Bather as Rhynchonella subtetrahedra, Dav., a species previously 
found in Somaliland where it is associated with others recorded 
from Abyssinia by Aubry and Douvillé.? 
This specimen, therefore, shows that while the main Archean 
plateau has never been below the sea, it was greatly depressed 
in Jurassic times, during which the sea rose upon its flanks and 
probably extended as a strait between the plateau of Somaliland 
and that to the southeast of Lake Rudolf. 
The next series represented is that of the volcanic rocks which 
1 J. W. Gregory, A Note on the Geology of Somaliland. Geol. Mag. Dec. 
vol. iv. 1896. p. 290. 
2 Aurry & Douvillé. Esquisse géologique du royaumedeSchoa_ Bull. Soc. 
géoly Mrance, ser. 3,1t. xiv. 1607, p- 230: 
