Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/25

 Rh of the Anfroques is probably of a similar structure, and this is somewhat pointed out by their granitiform outline.

SERCQ.



The little Island of Sercq lies six miles to the east of Guernsey, and is rather more than three miles in length. Its extreme breadth is not more than a mile and a half, and its average breadth not quite a mile. In one part, it is not many yards wide, being nearly divided into two portions, connected only by a high and narrow ridge. A small island, l'Isle des Marchands, lies on the west side of it, and sundry detached rocks surround it on other sides. Though of such small dimensions, it is more interesting to a mineralogist than the other islands, not only from the greater variety of its rocks, but from the more perfect exposure of its formation that is afforded by the abrupt cliffs which bound it on all parts. Unlike Guernsey or Alderney, it is a table land, having no declivity to the sea at any part, except a small descent at its northern extremity. The cliffs by which it is bounded are from one hundred to two hundred feet high. Except the Isle des Marchands which I mentioned, the western shore is so abrupt that large ships may range it very near without hazard. The eastern shore is less clean, and is beset with ridges of rocks running far out into the sea. The bottom is rocky. The eastern side of the land is also pretty uniformly about one third lower than the western, or it has a tendency to rise towards the west. In a general view the western side is of a trap and schistose formation, and the eastern of a granitic. It is intersected by veins of greater magnitude, and a more decided character than Guernsey, Alderney, or Jersey. The surface of the island though high, is every where intersected by deep vallies;