Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/163

 Rh Alderney, and the adjoining coasts of France. If it were attempted to determine the epoch when the land of Cornwall was separated from the opposite coast of the Continent, and consequently the epoch of the formation of the British Channel, we must, in order to diminish the resemblance as little as possible, fix the date of that great event, immediately posterior to the deposition of the granite, a period lost in the darkness of ages.

Mean Cliff, situated a little to the E.N.E. of the Land's-end, is also entirely composed of granite, and is one hundred and eighty eight feet high: at the bottom of it is a rock curiously shaped, called by the inhabitants, the Irish Lady.

In descending from Mean Cliff to White-sand Bay, we passed a small village called Escales, at the north end of which we found the rocks laid bare by the sea at low water, to be compact grauwacke: that rock may be traced for some distance under the sea. The same common grauwacke again occurs on the sea-shore a little further to the north. The point of land called Cape Cornwall, stretching out to the west, and which may be considered as the western limit of the northern portion of the mountain chain, is entirely composed of grauwacke, although it is two hundred and twenty-nine feet high, while, at the cliffs East of the cape, the same rock does not rise higher than ninety-three feet.

Advancing from Cape Cornwall into the interior of the country by St. Just, many blocks of schorl rock are found scattered on this part of the granitic plain, particularly amongst the rubbish of some old tin mines, which are now scarcely worked. Though quartz be disseminated in small crystals through the mass, it sometimes also