Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/17

 Rh regularity of their position gives them in some places, where their edges are exposed, a form so apparently columnar, that they might at a distance be mistaken for basalt: and when a succession of these ribs appears cropping through the grass, the appearance as of the skeleton of a mountain is exhibited. The cliffs give no opportunity of observing on what bottom this sandstone rests, as the tide flows high round them. I have remarked that it becomes finer and whiter as it approaches the south-west, that is to say, the strata which in their original horizontal position were undermost, are the whitest and finest. They, here also, approach nearer in their nature to a sandstone flag; acquiring a schistose fracture, though incapable of being raised in large masses. The stone is however easily quarried, and breaks naturally into masses having their sides slightly inclined, or absolutely rectangular. It is therefore well calculated for architectural purposes; and abundance might be procured at a small expense, very nearly adapted for squared building without the assistance of the chisel. The few in closures which are used in the island are built of this stone without mortar.

The principal varieties of the stone that I have been describing are the following.

1. White—very coarse—the quartz cemented by a clay the produce of the felspar.

2. The same—red—and with distinct grains besides, of felspar imbedded in it.

3. Dark red—and containing mica.

4. The felspar so distinct as to reapproach to a fine-grained granite.

5. A variety consisting of very minute grains, and to the magnifying glass exactly resembling a granite.