OYSTERS, Fossils. The largest bed that is known of
fossil oysters is that near Reading in Berkshire. They are entirely shaped, and have the same substance with the 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 crumbly PAN. Trans. marble, and a large portion of sand. Under them is 100 to 1. a thick stratum of chalk. They all lie in a level bed; 14-45. and the strata above the shells are natural, and appear never to have been dug through till the time of finding the shells.
The oyster-shells and green earth united make a stratum of about two feet thick; and over this there is a much thicker stratum of a bluish and very brittle clay; but neither has this ever been dug through, except where the shells are found. This is vulgarly denominated pierey-clay, and is esteemed useless. This clay-bed is about a yard deep, and above it is a stratum of fuller's earth, about two feet and a half deep; it is extremely good, and is used by the clothiers. Over this there lies a stratum of a fine white sand, unmixed either with the clay or fuller's earth: this is near seven feet deep, and above it is a stratum of a stiff red clay, of which tiles are made. This is again covered with a little vegetable mould; the depth however of this stratum of tile-clay cannot be ascertained, on account of the unevenness of the hill. These oysters are occasionally found whole, but most frequently in single shells. When they are in pairs, there is generally some of the green sand found with them: they seldom stick very fast together; so that unless very carefully taken up, it is not easy to preserve them in pairs.