occasional lenticular bands of a siliceous stone called ‘ chert.’ Its upper beds are dark, and produce black marble; some beds are reddish, and variegated. The whole mass attains a thickness estimated by the Government Geological Surveyors at 5000 feet, and appears to be composed of remains of corals, crinoids, and molluscs. 1 Towards the North of England the Carboniferous limestone is split up into several separate layers, with intercalated beds of shale, sandstone, and coal, 2 which in Scotland assume a high degree of importance, giving rise to the Lower series of coal and iron stone measures; while the beds of limestone dwindle down to a few thin bands, chiefly useful for affording hydraulic lime and cement. 3 Throughout this region, the Carboniferous limestone is rarely employed to any extent as a building stone ; its chief use being for the manufacture of mortars, cements, marbles, and for fluxing iron-ore. As the grits and sandstones of the Millstone and Yoredale beds generally occur in the neighbourhood of the limestone, they are generally preferred as a material for building, for which they are better adapted. 1 Hull, ‘ On the Distribution of the Carboniferous! Strata, &c.,’ Journ. Geol. Soc. LonJ. xviii. 137. See also Horizontal Sections of the Geol. Survey, Sheet 42. 2 Professor Phillips’ Geology of Yorkshire. 3 Such as the Arden limestone, near Paisley, and the Garnkirk, and Burdiehouse limestones near Coatbridge, and Edinburgh.