Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/47

Rh had been employed the whole time the works were carried on be correct, they came to the primitive rock in sinking a shaft forty yards deep. There the granite was found to form the north side of the vein, the galena adhering to it, while the south side was a stratified rock, which I shall hereafter mention. Whatever may be the depth at which the primitive rock was first remarked, there can be no doubt as to its existence, from the multiplicity of pieces of all sizes I found among the rubbish of the mine, and which were pointed out to me as such by the miner himself.

The rock is of a coarse grained texture, somewhat loosened, chiefly composed of quartz concretions, with reddish and decayed felspar along with some plates of white mica.

The mean specific gravity of the different sorts of granite above mentioned, is 2,81. From the granite above described, we come at once to the clay slate formation. The subsequent or intermediate members to granite in the series of the primitive rocks, viz. gneiss and mica slate, being either wanting absolutely, or if they exist at all, having escaped my attention, or being for the present concealed from our sight.

The clay slate formation in the Isle of Man does not appear to belong to the oldest kind of Werner. It is almost limited to the high ground occupying Snei-feldt, Bein-y-phot, South Borroilva, and Cronk-ne-liry-Lhaa. It also occurs at Mount Pellier as hone stone; at Peel-hill and Balla-Gawn, as roofing slate; and as a reddish