I04 THE ANTIQUITY OF MAN 
indicated, although Tilbury is a few miles lower down 
the river, and on'the opposite or northern bank. Then 
comes, in point of antiquity, the low or 20-foot terrace — 
the terrace in which the Hailing man of the Aurignacian 
period was found, but 1 must also state that the representa- 
tion of this terrace at Crayford has been washed away 
by the Thames long ago. Then, above the level of the 
low or 20-foot terrace come the Crayford brick earths, 
representing a still older deposit of the Thames — the 
CHALK 
HALUING 
tilbury- 
Fig. 37. — Diagram showing the submerged bed, the low or 20-foot terrace, the 
middle or 50-foot terrace in the valleys of the Thames and Medway (after 
Hinlon, Kennard and Chandler). 
middle or 50-foot terrace. We must examine the structure 
of this terrace. In the first place, its lowest layer or 
stratum is made up of gravel — the ballast gravel which 
marks the ancient bed of the river. That gravel rises now 
30 feet above the present level, not of the bed of the 
river, but of the river itself. When the beginnings of 
the middle terrace were being laid down, the Thames was 
flowing on a bed at a level more than 30 feet above its 
present bed. Were the Thames to resume the level of 
its ancient bed it would bury a considerable part of 
London by its sediment. Then, above the gravel bed, 
follow strata of sand, about 14 feet in depth, indicating 
