i 
. 
4 
L 
17 
to the previous pebble bed, the next succeeding stratum, that of the 
London clay, a thick deposit of stiff tenacious clay, from 200-ft. to 
500-ft. thick, must have been derived from the wear and tear of 
some old Southern and Western land, during a long period of 
time. It is of great thickness and extent, for it reaches from 
Hungerford to Canterbury on the south, and to Harwich on the 
north, varying in breadth from a few to 50 miles, and forming the 
marked deposit of the London basin. It may have extended all 
over the area) now occupied by the intervening chalk ridge, for it 
is found in outliers on the Downs; in the Hampshire basin, and 
also in the Isle of Wight. Eastward, it passes under the German 
Ocean, for it occurs in Belgium, and hence afforded one of the 
suggestions for the submarine tunnel, but only reaches France, 
near Dieppe, and is not found in the Paris basin, where it is 
doubtfully represented by other strata. 
Not only does the London clay indicate great physical, but also 
considerable climatal changes. There was evidently a much 
warmer climate than in the preceding part of the tertiary period, 
possibly resembling that of the chalk time, as is clearly shown by 
its well-marked Fauna, which is chiefly of marine origin. It 
had, however, its land conditions—and here the studies of the 
naturalist assist the geologist, reasoning from data of the present 
known to us, we may fairly infer the conditions under which its 
accumulations took place. A muddy deposit is usually unfavour- 
able to certain forms of life ; hence the reason, perhaps, of the 
comparative rarity of Sponges, Coral, and Echinoderms, although, 
in some localities, the Pentacrinus flourished. The molluscan 
life (800 species) was rich in genera, many now restricted to 
tropical seas, as Volutes, Cones, Cowries, Pleurotoma, Fusus, 
Cassidaria, Venus, Pholadomya, &c., while no less than nine 
species of the tropical genus, Nautilus (only two now existing) were 
associated with other curious forms. Of fishes, they were many 
forms, about 100, some belonging to the Elasmobranchs, such as 
sharks, rays, and largely to the Teleosteans, which here increase in 
number, although foreshadowed at the close of the chalk period 
by two or three forms, as Beryx and Osmeroides ; the Reptiles are 
represented by Crocodiles, Chelonians, and Snakes, the latter ap- 
pearing, for the first time, in the geological series, and the study 
of these forms and their habits, as shown by Professor Owen, are 
of much interest. The crocodiles and turtles refer to land condi- 
tions. We find marine, soft or river turtles, and also tortoises. 
No less than 10 species of marine turtles have been found in the 
London clay of Sheppy ;- while, at the present time, there are only 
about five known species, and these widely distributed. Those of 
us who may believe in the ancient Pythagorean philosophy, might 
infer that the love of the civic Alderman for turtle may be due 
to the spirit of the old Sheppy chelonian not having been lost 
