III.—The Residual Earths of British Guiana commonly Tremed ‘Laterite’

Extract

The Christianburg and Akyma deposits afford excellent examples of the highly aluminous or bauxitic type of laterite formation. They here occur as parts of a residuary deposit derived from the decomposition in situ of an igneous rock, probably a porphyrite or a tuff, an almost pure quartz-sand, and masses of bauxite containing in the more aluminous varieties from 92·6 to 94·4 per cent. of the hydrates of alumina and in the ferruginous ones 64·6 per cent. of the hydrates of alumina with about 24 per cent. of the oxides and hydrates of iron.