Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/220

 Preen and Kenley. The texture of this stone is loose, so as readily to admit the infiltration of water, in consequence of which the hornblende decomposes into a yellowish-brown clay, and then the rock is apt to be confounded with clayey sandstone-slate.

The space between the outburst of this bed and of the quartz-grit, hereafter to be mentioned, is a valley, the bottom of which is occupied by patches of a sandstone, varying considerably in its external appearance, presenting no marks of stratification or regular position, and (as I apprehend) not belonging to the series of strata, but quite superficial and composed of the materials of the two beds upon which it is situated, together with small shells, either entire or in fragments, belonging chiefly to the genus cardium. It always contains mica, but for the most part in small scales, and dispersed irregularly through its substance.

The quartz-grit, which is the next bed, consists essentially of quartz in rounded grains from the size of a pin's head to that of an egg, In some parts it is so entirely free from admixture as to be well fitted for the finer kinds of porcelain, since it acquires a snowy white colour by calcination ; but more generally it is mixed with angular fragments of the bed which lies beneath it, in a state of greater or less decomposition. Its northern boundary is the Arcal hill, the eastern side and top of which it entirely covers; it then skirts along the eastern side of the Wrekin, overspreading it to about one third of its height with conical hillocks. It is interrupted by the valley of the Severn, but re-appears on the south of this river, constituting the high ridge whereon are situated the parks of Acton-Burnwel, and Frodesley; it then runs parallel to the Lawley, but separated from it by a deep valley; the ridge then rapidly declines in height, and applies itself on the eastern side of Caer Caradoc (as it had before done on the Wrekin) Accompanying this hill along its whole length, and then terminating.