RECENT.--The alluvial deposits of most river valleys and some estuaries
still in course of formation, containing fossil shells and mammals, all
of living species.
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.