Miss C. A. Raisin—Geology of Africa. 441 
which is a compact rock, probably from near the edge of an 
enstatite-dolerite mass. 
The sedimentary rocks seem to belong to at least two periods. 
Some strong grits and conglomerate, lithologically resembling the 
Welsh Cambrian or Scotch Torridonian, are probably of old Palzo- 
zoie, or even earlierage. Differing from these are quartz-sandstones, 
sometimes ferruginous, which are very similar to the Nubian sand- 
stones. Various argillites, mudstones, and muddy quartz-felspar 
grits are found, some exhibiting slight results of contact alteration, 
due, very possibly, to the adjacent dolerites. 
In the first part of the journey from near Kambia, along the 
Scarcies River, gneissose rocks were exposed, and at Sasseni the 
ancient grit, derived partly at least from old Archean schists, and 
resembling, as previously stated, some early conglomerates of our 
own island. 
The Kofiu Mountain rising to a height of 3200 feet seems to be 
mainly formed of gneiss, probably Archean, capped by “ undisturbed 
horizontal sandstones” of a Nubian type “800 feet thick.” Along 
the upper part of the Scarcies River in Mount Jambi Buyabuya. 
are compact diabase, ophitic dolerite, olivine dolerite, and some 
sedimentary rocks. In the Talla Plateau (2000 to 3500 feet, about 
lat. 10° N.) igneous rocks of a basic type seem to be well developed. 
Dolerite apparently forms the top of the plateau for 20 or 30 miles, 
ending at one place in “an abrupt cliff 400 feet high.” The summit 
of the Gonkwi Mountain (altitude 3000 feet) consists of an enstatite- 
dolerite with one partly spherulitic specimen; and associated with 
this mass and other igneous rock are argillites and gritty mudstones, 
some showing slight contact alteration. Near Kundita and Falaba 
(altitude 8500 feet, about lat. 10° N.) micaceous gneiss is common, 
and here also a hyperstheniferous diorite or norite occurs, containing 
amblystegite. 
On the return journey to the coast at a point further south near 
Sierra Leone, some crushed specimens of schist and a mylonite, 
and some igneous rocks of basic or somewhat basic composition were 
collected. One dolerite has become a richly ferruginous and probably 
workable ore by the formation of iron oxide apparently replacing 
a pyroxene, the felspar having been replaced by a pinite-like 
mineral. Iron oxide frequently also is deposited in the usual way 
in sandstone, often forming an “iron pan” or “ laterite.” 
Thus we find a general resemblance in many points between the 
rocks collected towards the extreme east and west of the African 
continent.t Above the foundation stones of gneiss and similar 
crystalline rock, rest the sedimentary deposits which (except the 
probably more ancient conglomerate and grit) seem mainly to be of 
the uniform Nubian type. The associated igneous rocks, whether 
they are intrusions or lava flows, are often lithologically similar in 
both districts. 
1 See also Phil. Trans. 1883, On a Collection of Rock Specimens from the Island 
of Socotra, Prof. T. G. Bonney. Also Grou. Mac. 1888, Dec. ITI. Vol. V. p. 414, 
C. A. Raisin, On some Rock-specimens from Somali Land; p. 504, On some Rock- 
specimens from Socotra. 
