_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 _Limnoea 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.
_b._ _Middle Eocene_, or the _Bagshot Beds_, composed of sands and
clays. The beautiful coloured sands of Alum Bay, the sands of the Surrey
and Hampstead Heaths, are familiar examples of the beds of this age.
Very few fossils indeed have been found in them. The clay-beds on the
contrary as seen at Barton and Hordwell on the Hampshire coast and again
in the Isle of Wight, abound with shells belonging to genera such as
_Conus_, _Voluta_ and _Venus_, that inhabit warm seas. With them are the
Nummulites, looking externally very like buttons, but on the inside
divided into innumerable chambers in which the complex animal that
formed the nummulite dwelt.
_c._ _Lower Eocene_, the well-known London clay, may almost be said to
compose this division, for the underlying sands, gravels, and clays are
in mass comparatively insignificant. The London clay contains plenty of
fossils, only as they are disposed in layers (_zones_) at a considerable
distance apart, they are not often hit upon. Layers of Septaria or
cement-stones are of frequent occurrence. Sheppy is the great locality
for London clay fossils, as the sea annually washes down large masses of
the cliffs and breaks them up on the beach. A great many fossil fruits
and seeds, remains of crabs, shells of Nautili, Volutes, and other
mollusca, besides turtles, a species of snake, a bird with teeth, and a
tapir-like animal, have at different times and in various places been
found in this deposit, which sometimes attains a thickness of over 400
ft. The "Bognor Rock" is a local variety of the basement bed of this
formation.
[Illustration: _Aturia Zic-zac_ (from the London clay).]
The MESOZOIC or SECONDARY rocks embrace a series of limestone, clays,
sands, and sandstones that on the whole are well consolidated. The main
mass of them lies to the west of a line drawn across the map of England
from the mouth of the Tyne, in Northumberland, southwards to Nottingham,
and thence to the mouth of the Teign in Devonshire. In the south-eastern
counties they underlie the tertiary rocks of the London and Hampshire
basins, as they are called, at no great depth from the surface. Outlying
patches of secondary rocks occur in Scotland, where they are found near
Brora on the east coast, and in the islands of Skye and Mull on the
west. In Ireland they are scantily represented round about the
neighbourhood of Antrim. The secondary rocks are divided into--