Calcareous Sandstone

Masses of this, from about 8 inches to 2 feet thick, were found at near twelve feet deep in a light gravelly stratum, in cutting the canal at the Isle of Dogs. The decomposing shells have apparently undergone a change, by means of subterraneous heat causing them to combine with the sand and pebbles. Some of the shells I believe are new to Great Britain, both in the natural and fossile state. These are the gibbous Arca, at the lower corner on the right hand, the hinge and cockle-like edge of which are seen distinctly above it; the oblong Arca resembling a Mytilus, on the left side, showing part of the hinge, which I have not seen in any other specimen. The decomposition of this shell, and the Turbo near it, are more chalky than the others. The oblong oyster shell at the top retains its pearly lustre. Other shells have only left their impressions or cast. Some of the pebbles are cracked with the heat, and their interstices filled by calcareous matter.

The whole forms a calcareous sandstone, with very little variation, and is of a pale brown colour^*. The parts being distinct, it forms an instructive specimen, and will serve to explain more obscure ones.