PEOCEEDLNGS OF GEOLOGICAL SOCIETIES. 
61 
the mineral character is the same throughout, it follows that there must 
have been a slow subsidence ^oing on, to make up for the shallowing of the 
sea by the continuous deposition of sediment, and thus to allow the life of 
the age to keep the same during the whole time of deposition of these hun- 
dreds of feet of clay, which it could not do if the depth of the sea were so 
much lessened as would be the case without subsidence. 
The only place where any nimiber of fossils have been found in the Lon- 
don Clay in Kent, is the Isle of Sheppey, where, however, the cliffs have 
yielded a rich harvest both of species and specimens. These, which are 
from the higher part of the formation, give evidence of the existence in 
those long-past ages of corals, star-fishes, sea-urchins, an abundance of 
Crustacea (crabs, lobsters), often forming the nucleus of septaria, mollusks 
in great plenty, fish (especially sharks, the teeth of which are very common), 
and rays and reptiles (turtles, tortoises, crocodile, and serpent.) The re- 
mains of a small pachydermatous mammal have been found near Herne Bay. 
The most remarkable of the Sheppey fossils, and which are far less common 
elsewhere, are the plant-remains. These are chiefly of the leguminous 
and coniferous orders and palms, and consist of fruits, seeds, and stems. 
They are in iron-pyrites (sulphide of iron), and therefore very difficult to 
keep, as that substance often decomposes when exposed. They show that 
the neighbouring land on which they grew must have been much warmer 
than our present temperate climate ; and this evidence is strengthened by 
that of the remains of the MoUusca, amongst which the univalve iN'autili, 
Cones, Cowries, and Volutes show that the sea in which they lived must 
have been in a warm climate. Shells of many other genera occur, such as 
Fusus, Xatica, Pleurotoma, Rostellaria, and the bivalves Cardium, Pec- 
tunculus, and Teredo, a great deal of the wood having been bored by the 
last. These shells, like the vegetable remains, are in the state of casts in 
iron-pyrites. 
Tile middle and lower beds of the London Clay, near "Whitstable and 
Herne Bay, have yielded fewer fossils. 
A noteworthy feature of the London Clay cliffs is the frequent occur- 
rence of landslips ; nearly the whole face of the sloping cliff being generally 
made up of the fallen masses. In dry summer-time the clay is shrunk by 
the heat, and deep cracks are formed; when rain falls, much water finds 
its way down these cracks, loosens the clay, and makes it slippery, so that 
masses can more readily fall down. The destructive action of the weather 
is, however, greatest in the winter, when the water in the deep cracks 
freezes, and the vast force put forth in its expansion, on becoming ice, 
loosens the beds, which would then tend to slip down after a thaw. Early 
in the present year (18(33) a slip occurred which threw a long strip of land, 
about two acres in extent, some way down the cliff: the young wheat was 
growing very well in its strange position. 
5. TA(? Lower Btiffshot Sand occurs in the form of a thin outlier on the 
highest part of the Isle of Sheppey ; the only place in Kent where the 
London Clay is capped by this formation, which has been worn off alto- 
gether in other parts of the county. The sand is light- coloured, more 
clayey towards the bottom, and generally passes into the sandy clay form- 
ing the uppermost part of the London Clay. It may be seen for more than 
a mile along the cliff near Minster, and is at the most some 30 feet thick. 
Although of so small ext-ent and thickness, this outlying mass of sand is 
of much geological value. Firstly, it proves that the Bagshot series once 
spread over these parts, as the outliers at Rayleigh and elsewhere on the 
opposite side of the Thames prove its former extension over Essex ; and, 
secondly, it enables us to calculate the thickness of the London Clay from 
