Quaternary, Post-Pliocene, or Pleistocene.—1. Including the raised beaches around the coast, the older gravels of river valleys and the cave deposits, in all of which the shells are identical with those living in the rivers and seas of to-day, whilst the animals are many of them extinct, only a few being now found living on the spot.
2. The glacial drifts that cover all England north of the Thames, and which consist of sands, gravels, and clays, full of big angular stones frequently flattened on one side, scratched and sometimes polished from having been fixed in moving ice and forced over other rocks. A very interesting collection of these "boulders," as they are called, can be easily made, for they belong to almost every formation in England, and have some of them been brought from great distances, whilst the number and variety obtainable from a single pit is astonishing.
Cainozoic, or Tertiary.—Beds of this age, in England at all events, are for the most part made up of comparatively soft rocks, gravels, sands, and clays, and are found in the eastern and south-eastern counties. They are divided into—
1. Pliocene, mainly consisting of a series of iron-stained sands, with abundant shell remains, and locally known as "crags." The shells are very partial in their distribution, the beds in places being almost entirely made up of them, whilst in others scarcely one is to be found. The great majority are of the same species as many still living. The Pliocene is subdivided into three groups:—
a. The Norwich Crag Series, sometimes called the "Mammaliferous Crag," as at its base the bones of mastodon, elephant, hippopotamus, rhinoceros, and some deer have been found. The shells in it are such as still abound on the beaches of the eastern coast to-day—whelks, scallop shells, cockles, periwinkles, etc.
b. The Red or Suffolk Crag, its two names indicating its characteristic colour (a dark red-brown) and chief locality. From the base are obtained the celebrated phosphatic nodules miscalled "Coprolites," whence is manufactured an artificial manure, and with them are found the rolled and phosphatized bones and teeth of whales, sharks, etc. Amongst the shells the Reversed Whelks (Fusus contrarius), Fecten opercularis, Pectunculus glycimeris, several kinds of Mactra and Cardium, etc., are the commonest. Walton-on-the-Naze, Felixstowe, and Woodbridge are the best known localities.
c. The White or Coralline Crag is generally of a pale buff colour, and is in places almost entirely composed of the remains of Polyzoa. These (formerly called Corallines, whence the name Coralline Crag) are beautiful objects for a low-power microscope, or pocket lens, and are easily mounted in deep cells on slides. The bits of shell and sand that stick to them should be carefully removed with the point of a needle. A very large number of shells occur in this crag: of bivalves, the Pecten is very abundant, and its valves are frequently thickly grown over with Polyzoa; Cyprina Islandica, Cardita Senilis are also plentiful; and of univalves, the genus Natica is common. The Coralline Crag is best seen in the neighbourhood of Aldborough, Orford, Woodbridge, and other places in Suffolk.
2. Miocene, possibly represented in the British Isles by a small patch of clays and lignites at Bovey Tracey.
3. Eocene, divided into—
a. Upper Eocene, consisting of a series of very fossiliferous sands, clays, and limestones, exposed in the cliffs at the eastern and western ends of the Isle of Wight and on the neighbouring coast of Hampshire. They are partly of freshwater origin, when they contain the remains of freshwater shells such as Limnœa Paludina, Planorbis, etc.; partly of marine origin, when shells belonging to such genera as Ostrea, Venus, etc., take their place; partly of estuarine, when the brackish water mollusca are found with bones and scutes of crocodiles and tortoises.