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Medical History of the 1841 Niger expedition
|► 1841 Niger expedition ► Medical history||Section 3|
EXPEDITION TO THE RIVER NIGER
DURING THE YEARS 1841-2.
Geology of the Niger.
The following account is condensed from the notes of Dr. Stanger.
The Delta of the river Niger is a flat tract, composed of clay and sand, in places containing minerals and much vegetable matter. It may be considered to extend to Aboh, a distance of 120 miles from the sea.* The banks of the river are elevated only a few feet above its level, and the interior is swampy. From the soil we prognosticated granite in the interior. The land gradually rises from Aboh to Iddah, but is still swampy, and there are no rocks: the cliffs at Iddah 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 three degrees to the south-east; 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 examination, one fossil only, and that a very obscure one, was met with in the sandstone: it has some resemblance to Pollicipes. The cliffs at Iddah are formed by the outcrop of a ridge of hills running north-east and south-west. From Iddah to Ikori 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 Ikori strata of mica slate, dipping eighty-five degrees due west, appear standing up in high masses on the right bank of the river, near which bank, opposite to Ikori, 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 composed of granite, 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 hornblende. At Okazi the granite is more largely crystalline, and contains very beautiful opalescent felspar.
The granite extends to Adda Kuddu, and at that place it is mixed up and complicated with gneiss, which dips at an angle of sixty degrees to the south. The gneiss contains veins of granite running in all directions. Further on the granite again contains imbedded masses of gneiss. From Adda Kuddu, 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, and 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 on the mica slate.