Fig. 675.—Sketch-map of various geological formations.
The Oolite formation (see Map) occupies a stretch of country in England extending from Yorkshire into Dorset. The Great Oolite holds the Fuller’s earth, and the Bath stone is also well known. The Stonesfield slate holds many remains of reptiles. It is a kind of shelly limestone, and is used for roofing purposes. The Forest Marble (so called from Wychwood Forest) is a sandy limestone holding marine fossils. It is used for ornaments. The Coral Rag and Oxford clay are rich in fossils, and the former, as its name implies, is composed of ancient coral reef. The Portland beds produce the well-known building stone. The Purbecks, of which there are three divisions, appear to have been deposited in fresh water, and occur in Dorsetshire.
All the Oolite strata supply organic remains. We have plants and ferns, reptiles, and a number of new genera of conchifera and cephalopods, star-fish, urchins, and the enormous bats, and the terrible megalosaurus, and the cetiosaurus, steneosaurus, and pliosaurus, of enormous size. One very remarkable bird has been found in the Bavarian limestone of this period; it is called the Archæopteryx, which is described as having a leg-bone and foot like the familiar birds, but the tail is lizard-like, with feathers springing from each joint. Sponges, corals, and fish, and many other forms of animal life are found in the Oolites. The reptiles must have had it all their own way in this period, for there were both carnivorous and vegetable feeders, and teeth of the pliosaurus have been found which measure fifteen inches, the jaws being six feet long. We have seen that corals must have built up their reefs in the waters, which then overlaid the land we call the United Kingdom.
There must have been great changes during this period, and the strata are chiefly marine. The Wealden formations are the exceptions, and in the fresh-water deposits insect forms abound. The appearance and variety of animal and vegetable life must have been curious and interesting.
The Weald or “Wold” of Kent is often spoken of, and it extends with the Surrey and Sussex Wealden formations for some distance. The strata are of fresh-water deposition, differing in this from the chalk, although the Wealden beds are included in the Cretaceous Group, which is composed as follows:—
| Lower | ⌈Wealden. ⎢Greensand. ⌊“Gault.” |
| Upper | ⌈Upper Greensand. ⎢Chalk Marl. ⎢Chalk (without Flint). ⎢Chalk (with Flint). ⌊Maestricht. |
The “Wealden” formation is divided into Hastings sand and Weald clay. The former consists of clay and sandy beds, and is observable at Hastings, and in the neighbourhood of Tunbridge. The Weald clay consists of blue and brown clays, with sandstone, and the limestone known as “Sussex Marble,” which is formed by the paludina of the rivers. There is another division often seen in Dorsetshire, and called the Punfield beds, which partake both of marine and fresh-water remains, which are distinct in the true Wealden and cretaceous formations, the former being of fresh, and the latter of salt-water origin.
Fig. 676.—Echinus (Hemicidarus intermedia, Chalk).