Fossil. The largest bed that is known of fossil oysters is that near Riding in Berkshire. Their shape is entire, and they consist of the same substance with recent oyster-shells; and yet since the oldest histories that mention the place give an account of them, we must suppose they have lain there for a long time. They extend over no less than six acres of ground; and just above them is a large stratum of a greenish loam, which some writers call a green earth, and others a green sand. It is composed of a crumbling marle, and philet; a large portion of sand. Under them is a thick stratum of chalk. They all lie in a level bed; and the strata above the shells are natural, and appear never to have been dug through till the time of finding the shells.