ANCIENT AND EXTINCT BRITISH QUADRUPEDS. 1238 
the thickness of a shilling, will often suffice to preserve the thigh- 
bone of an Elephant. It is now generally supposed that many of 
the rivers of our southern and eastern coasts are but the head-waters 
of what were once much larger rivers before the severance of the 
islands from the mainland of Europe. The Thames is thought to 
have been one of the tributaries of the Rhine; and, as will be 
noticed in the sequel, it is seldom that oyster-dredging is prosecuted 
with vigour on the coasts of Norfolk and Suffolk without quantities 
of bones of extinct quadrupeds being brought to the surface. When 
the separation in question took place is not altogether clear; that 
England and Europe were united, however, at the close of the 
glacial epoch seems pretty certain, else how could such animals as 
the Elephant and the Lion have reached the British Islands? The 
probability is that there was a highway at the Straits of Dover, 
which may have disappeared before the Lions and Elephants died 
out on British soil. 
With the thaw of the glacial period the rivers doubtless became, 
then and long afterwards, subject to constant inundations, which 
covered large tracts of country, and formed deposits of sand, loam 
and clay, in which the animal remains are now found. London, for 
example, is built on deposits of the ancient Thames; and in many 
other situations where insignificant streams now exist, the banks 
are made up of vast beds of débrts stretching inland, and containing 
the bones of both extinct and living animals. Again, deep in the 
brick-earths of the Thames Valley, at Clacton, Ilford, Grays (Essex), 
and Crayford, remains representing herds of giant Oxen, Deer, 
Elephants, Rhinoceroses, &c., have been discovered from time to 
time, indicating that they had probably been drowned and carried 
down by inundations of the Thames. In the nature of the animal 
remains there is a general accord with those of river-bottoms and 
of the caves, thus showing that they were of the same geological 
period. But in the brick-earths, or lowermost strata of rivers, it 
sometimes happens that remains of animals are found distinct from 
any other species found in the upper beds and in the caves; in con- 
sequence, it has been surmised that the brick-earths may have been 
deposited during pre-glacial times, and therefore contain the animals 
of that epoch. Some idea of the animals which frequented Wales, 
South and South-Western England, the Thames Valley, Yorkshire, 
and the South of Ireland may be gathered from the following :— 
In several caverns in Glamorganshire remains of man have been 
