Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/126

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In Cornwall, as in the Hartz, the covering of grauwacke never rises very high, and we find that here, the more elevated points, although their absolute height be not very considerable, are left bare,

Here also, as in other countries, the two varieties of grauwacke, are uniformly found connected with one another: they in general cover the transition limestone, whereas secondary greenstone and clay-slate occur in it in subordinate beds, and perhaps the formations of serpentine, of diallage with felspar, and of talcose slate, of whieh I shall afterwards speak, are similarly situated.

Though the cliffs at Stonehouse are of limestone, nevertheless Mount Edgecumbe, which is only separated from them by the Hamoaze, belongs to the grauwacke formation. We here find that rock passing from the state of a coarse argillaceous sandstone, of a reddish colour, not effervescing, and stained by oxide of iron, to that of a fine-grained grauwacke-slate, with red veins, giving it the appearance of ribbon jasper. It occurs in strata, dipping S.S.E. at an angle of about 65° or 70°, which is nearly the same as that of the limestone cliffs of Plymouth harbour. The stratification is best seen on the south side of Mount Edgecumbe about half way up; and especially from the great terrace to the arch, and beyond that on the way to the zig-zag walk. At the top of the hill the grauwacke becomes less distinctly stratified, and begins to separate into rhomboidal pieces. Maker Heights, Rame Head, Higher Blarick in