Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/19

 Rh undiminished force of the wind and the sea, it has undergone considerable changes, and many detached rocks of rude forms are the consequence. And on this side it is in many places so thoroughly decomposed, as to have formed a white, powdery, siliceous soil, much resembling tripoli.

The whole of this porphyry has a hornstone basis, and is either red, grey, or white. Together with the felspar, it frequently contains imbedded grains of quartz. On the beach I picked up flints, and pebbles of different coloured hornstone. It is a necessary consequence of such an arrangement of rocks, that a great part of the soil of Alderney should be sandy. It is nevertheless well supplied with water, and produces good crops of grain and vegetables. Its valuable breed of cows is well known.

The precipitous rock Ortac lies a mile and a half to the westward of Alderney. It is about an hundred feet high, and connected with a chain of rocks that stretches from Burhou. And at the distance of seven miles in the same direction are the Casquets, remarkable for their well-known lighthouse, and consisting of many high and sunken rocks. I had no opportunity of visiting any of these, but was informed that they consisted of the same grit as the eastern end of Alderney. The figure of Ortac would however lead me to think that it was formed of porphyry, as its precipitous appearance is not so consistent with the tendency of the grit I have described. No organic remains have, as far as I know, been found in Alderney.

GUERNSEY.



The approach to Guernsey is also full of danger, from the number of the rocks, and the rapidity of the tides which surround it.