MOUSTERIAN PERIOD 105 
that the river was flowing more slowly — the land was 
subsiding, and the valley was being filled up. Above 
the sands come another series of beds, known as the 
Cyrena beds, containing in abundance the shells of 
certain molluscs and bones of small mammals. Then 
follow the typical brick earths — loamy deposits from the 
backwaters of a muddy and flooded river. From the 
gravel of the old river bed to the surface of the brick 
earth the deposits laid down by the river during a period 
of land subsidence amount to over 30 feet in depth. 
From the very beginning to the very end of this deposit, 
men who worked their flint implements in the Mousterian 
style lived on the southern bank of the Thames, for, 
at all levels of the brick earths, these implements have 
been recovered. Messrs Hinton and Kennard, and Mr 
Chandler, recognised that the implements were Mousterian 
in type in 1905,^ and their inferences were fully supported 
by the collection of implements which Mr Brice Higgins 
obtained from all horizons of the Crayford brick earths, 
and which have been described and recorded by Mr 
Reginald Smith. ^ 
The section of these brick earths as recorded by Mr 
Chandler and Mr Leach ^ (see fig. 37) throws a very 
definite light on the climate both before and after the forma- 
tion of the 50-foot terrace. Over the brick earths lies a 
deposit technically known to geologists as a drift or " trail " 
— a mixture of chalky blocks, gravel, sand, and sludge. 
Such a deposit results from the freezing of a surface soil, 
which in the thaw slips bodily down from higher to lower 
ground. After the Crayford brick earths were deposited, 
there evidently followed a cold period — marked by the 
formation of trail. We have seen, from the Arctic beds 
in the low terrace at the Admiralty buildings, and from 
Mr Warren's discovery in the low terrace of the adjoining 
Lea valley, that during the late Palaeolithic periods there 
was a return to a sub-Arctic climate. The drift or covering 
^ See reference, p. 107. 
- See Man, 1914, vol. xiv. p. 4 and p. 31. 
3 See Proc. Geol. Assoc, 1912, vol. xxiii. p. 186. 
