Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/18

 6 6. A granitel, consisting of quartz and felspar in equal proportions.

7. A similar stone with a much less proportion of felspar.

8. No felspar at all—a fine white sandstone.

All these varieties are evidently the produce of the disintegration and reunion of more ancient granites.

At a point on the southern shore, is a rock called La Pendante, resembling a square tower of masonry, and inclined at a considerable angle. It consists of portions of the strata I have been describing, and appears about twenty feet high.

Where the strata of grit cease, a vein, or an inclined stratum, of black granitel, composed of hornblende and quartz, is found; which appears to run straight, and in contact with them, in a N and S direction across the whole island, from l'Etat to Braie. This is a thick mass, but I could neither discover its dimensions, nor its points of contact with the grit. It is in some places accompanied by a fine-grained sienite of a compact nature; and by another, much disintegrated and shot with iron. Here and there also, are fissures filled with red and purple hornstone, and more rarely, fissures, or what appear such, filled with sandstone-schist and mica, and often assuming the appearance of micaceous schist. The grit, which is cut of by this mass of granite, does not here absolutely disappear; but various strata of it and the granitel, succeed each other, till the whole ceases, and is replaced by a mass of porphyry.

Of the mass of porphyry, the remainder of the island is formed. And it is the broad and perpendicular fracture of this rock, which causes the picturesque appearance of the western extremity of the island.

It appears to have a great tendency to wear before the effects of time. At the western point in particular, where it is exposed to the