Lower Oolites.
a. Cornbrash, a very shelly deposit of pale-coloured earthy, and rubbly or sometimes compact limestone with plenty of fossils. The commonest are Brachiopods, Limas, oysters (Ostrea Marshii), Pholadomyas and Ammonites. It is best seen in Dorsetshire, Somersetshire, and near Scarborough in Yorkshire.
b. Forest Marble and Bradford Clay. The former is an exceedingly shelly limestone, often splitting into thin slabs. On the surfaces of some of the beds may be seen the ripple marks the sea made countless years ago, and the tracks of worms and crabs that dwelt in the mud or crawled on its surface at a time when it was soft mud. The Bradford clay is a very local deposit, taking its name from Bradford in Wiltshire, where it is most developed, and its characteristic fossil is the pear-shaped Encrinite or "stone-lily" (Apiocrinus Parkinsoni).
c. The Great or Bath Oolite, comprising a series of shelly limestones and fine Oolites, or freestones. The latter are largely quarried in the neighbourhood of Bath, and used for mantelpieces and the stone facings of windows. The great Oolite is rich in univalve mollusca, amongst which may be noted a limpet (Patella rugosa) and the handsome, tall-spired Nerinæa Voltzii, numerous bivalves belonging to the genera Pholadomya Trigonia, Ostrea (O. gregaria), and Pecten, besides Brachiopods (Terebratula digona, which looks very like a sack of flour, and T. perovalis, etc.).
At the base of the Great Oolite are the "Stonesfield slates," so-called—a series of thin shelly Oolites, etc., that split readily into very thin slabs. They are principally of interest to geologists on account of the discovery in them of the remains of small insect-feeding and possibly pouched mammals. With these are associated the bones of that big reptile the Megalosaurus; the flying lizards called Pterodactyles; fish teeth and spines; lamp shells; oysters, a Trigonia (T. impressa); and the impressions of insects, including a butterfly, and of plants.
d. Fullers' Earth, a clayey deposit occurring in the southwestern parts of England, but not in the north. It abounds with a small oyster (O. acuminata) and Brachiopods (e.g. Terebratula ornithocephala), etc.
e. Inferior Oolite (including the Midford Sands). As these beds are followed across the country from the south-west of England to Yorkshire, they are found to change greatly in character. Limestone and marine beds in the south are replaced by sandy and estuarine beds in the north. Amongst other fossils from beds of this age may be found several Echinoderms, a crinkly lamp shell (Terebratula frimbriata), and a spiny one (Rhynchonella spinosa), bivalves belonging to the Genera Ostrea, Trigonia, Pholadomya, etc., and some very handsome Ammonites (e.g. A. Humphresianus).
