Geology of the West Coast of Africa. 219 



Coast Castle it is decomposed into a clay containing sparkling par- 

 ticles of mica, which are not unfrequently mistaken for gold. 



6. Grand Sesters. — The rocks here are gneiss cut through by gra- 

 nite, as at the river Sinoo. The felspar of the granite is opalescent. 



7. Niger. — The Delta is a flat swampy tract composed of clay, sand, 

 and much vegetable matter, extending to Eboe, a distance of 120 

 miles from the sea. The banks of the river are elevated only a few 

 feet above its level. From Eboe to Iddah, a distance of 100 miles, 

 there is a gradual rise of the country, but still swampy and similar 

 in constitution to the Delta. At Iddah the first rocks appear. They 

 are 185 feet high (barom. measure) and are composed of sandstone, 

 the strata of which are for the most part horizontal, but occasionally 

 dip at an angle of 3° to the S.E. This sandstone is fine granular, 

 and composed of transparent particles of white quartz. The upper 

 beds are highly ferruginous. The strata are cut through by joints 

 running in all directions. After the most careful search, one fossil 

 only, and that a very obscure one, was met with in the sandstone. 

 It resembled a Pollicipes. The cliffs of Iddah are formed by the 

 outcrop of a ridge of hills running N.E. and S.W. From Iddah to 

 Kirree the country is composed of sandstone of the same character, 

 more or less ferruginous in places. The character of the country is 

 that of elevated table lands, edged by cliffs, bordered by debris. At 

 Kirree, strata of mica slate, dipping 85° due west, appear standing up 

 in high masses on the right bank of the river, in which bank, opposite 

 to Kirree, is the Bird rock, composed of a mass of quartz evidently 

 imbedded in the mica slate. The mica slate rests upon the granite 

 composing Mount Soracte and the neighbouring hills, attaining a 

 height not exceeding 1200 feet. Beaufort Island is formed of gra- 

 nite which is decomposed so as to leave the surface very rough, 

 from the projection of felspar crystals. It contains little mica, and 

 is composed of felspar and quartz with a small quantity of horn- 

 blende. The soil between the blocks of granite is a rich vegetable 

 loam. The blocks are piled one upon another like masonry. At 

 Okazi the granite is more largely crystalline, and contains very beau- 

 tiful opalescent felspar. The granite extends to Adda Kudda, and 

 at that place it is mixed up and complicated with gneiss which dips 

 at an angle of 60° to the S. The gneiss contains veins of granite 

 running in all directions. Further on, the granite again contains 

 imbedded masses of gneiss. From Adda Kudda, up the river, as 

 far as was explored, the country is composed of horizontal sandstone, 

 generally more highly ferruginous than lower down. At Mount 

 Stirling the iron occurs in the form of pea-iron ore. The granite 

 appears to be the central axis, mica slate and gneiss occurring on 

 both sides, or dipping at great angles. The granite is the line of the 

 so-called Kong mountains, which in no case were observed higher 

 than 1200 feet. The sandstone lies unconformably upon the mica 

 slate. Dr. Stanger considers the phenomena observed on the Niger 

 to indicate three geological periods : — 1st, the eruption of the gra- 

 nite and elevation of mica slate and gneiss ; 2nd, the deposition of 

 the sandstone unconformably on the flanks of the mica slate and 



