Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/24

12 The hornblende in some places predominates so as to give a sort of hornblende porphyry, and in others, every other ingredient is excluded, and a hornblende rock alone remains. I observed some specimens, traversed by a derivative rock of the same composition, interspersed with minute grains of pyrites; the only trace of the kind I perceived in this island.

This stone is very hard and sonorous, and admirably adapted for building, as it easily breaks into squared masses before the hammer. It is more particularly fitted for paving, from its extreme hardness and toughness; and for that purpose it is exported in large quantities to London and to Portsmouth, by the name of Guernsey stone, or St. Sampson's stone.

A similar succession of rocks occupies the remainder of the coast to the town.

Such, as far I had opportunities of remarking, is the mineralogical structure of this island. The discovery of lime was much desired by the inhabitants, but there is no appearance of limestone.

Although the principal rocks are of a metalliferous nature, no metallic traces have at any time been observed.

It has been a common belief in England that emery was a product of this island, but of this I could neither obtain physical nor historical evidence.

The soil which is the produce of the decomposed gneiss is abundantly fertile, the ground being well watered, in a climate exposed to the first arrival of the Atlantic clouds. Springs and rivulets are therefore plentiful, and as is usually the case in siliceous countries, the waters are remarkably pure and free from saline impregnations.

Of Herm and Jedhout which are detached prolongations of the same rocks, nothing can be said which would not be a repetition of what I have remarked concerning Guernsey. The inaccessible ridge