A Manual of Elementary Geology / or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments

by Sir Charles Lyell

Cast of Diceras arietina. Coral rag, France.

Fig. 276.

Cidaris coronata. Coral rag.

Oxford Clay.—The coralline limestone, or "coral rag," above described, and the accompanying sandy beds, called "calcareous grits" of the Middle Oolite, rests on a thick bed of clay, called the Oxford clay, sometimes not less than 500 feet thick. In this there are no corals, but great abundance of cephalopoda of the genera Ammonite and Belemnite. (See [fig. 277.]) In some of the clay of very fine texture ammonites are very perfect, although somewhat compressed, and are seen to be furnished on each side of the aperture with a single horn-like projection (see [fig. 278.]). These were discovered in the cuttings of the Great Western Railway, near Chippenham, in 1841, and have been described by Mr. Pratt.[262-A]

Fig. 277.