Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/270



V. Coarse Shelly Limestone (Calcaire grossier).

This kind of rock I am rather anxious to introduce here, because it seems to constitute a formation by itself, which, I believe, was first pointed out by M. Brongniart, who has given us some very valuable information on the subject. This variety of limestone was thought to be very scarce in England, but I am now disposed to believe, that upon a further examination, it will be found to occupy a great extent of country, and will, by many persons perhaps, be considered as a continuation of the same strata or beds which exist on the opposite coast of France. I have observed it in the southern part of the Isle of Wight called the under cliff, in several places of the Isle of Purbeck, in the Isle of Portland, and, from some specimens which I have seen at the Geological Society's apartments, I have but very little doubt, that it exists also in the counties of Surry, Sussex, Oxford, Rutland, and Somerset. In France, it forms the bottom or basis of several extensive plains; such as that of the neighbourhood of Paris, and that of Caen in Normandy.

I have seen it alternating with a calcareous sandstone, with the oolithe, (oviform limestone of Kirwan), and with marl: passages of it may be traced on one hand to the calcareous sandstone, and on the other to the oviform limestone. At the quarry of Tilly Wym by Seacombe Cliff, to the east of St. Aldham's Head, and at Chapman's Pool near Encombe, as also in the Isle of Portland, it includes patches of a compact limestone of a greyish, or dark blue colour, which becomes harder as it passes gradually into a state of complete flint or