io6 THE ANTIQUITY OF MAN 
over the Crayford brick earths may have been produced 
then ; at least it was formed before the lower terrace was 
finished, for that terrace shows no disturbance of ice 
action in its upper strata. 
Not only is there a trail over the Crayford brick 
earths, but, as Mr Chandler shows in his section (fig. 37), 
and as has been recognised for a number of years, there 
are the most definite signs of another drift or trail — a 
frozen landslide — on the side of the valley, occupying a 
period in time prior to the deposition of the Crayford brick 
earths in which the tools and culture of Mousterian man 
are embedded. This earlier trail or ice-deposit is known 
in England as " Coombe rock " — a mixed, contorted 
mass of chalk, sand, and loam, the results of a partially 
thawed landslide. Even before the period of the earlier 
trail, Mousterian man was in the valley of the Thames, 
for under the Coombe rock occur his old work-floors. 
Five miles lower down the valley— almost opposite 
Tilbury — there is another deposit of brick earths, which, 
like those at Crayford, form part of the 50-foot or 
middle terrace. They occur on the western bank of a 
side valley by which the Ebbfleet enters the Thames, 
being exposed at an excavation or pit known as Baker's 
Hole (fig. s6y p. 161). Here,^ under the Coombe rock, 
were found several thousands of Mousterian implements 
— evidently representing a tool manufactory or workshop 
of this remote period. 
From the study of the deposits in the valley of the 
Thames, we are able to form some conception of the 
position which the Mousterian period occupies in the 
scale of prehistoric time. It is manifest that this period 
is older than the formation of the low or 20-foot terrace, 
for when the middle or 50-foot terrace is traced towards 
the river, it is found to dip under, and therefore to have 
been deposited before the lower or more recent terrace. 
Further, we see that it lies between two cycles of severe 
climate. The duration of the Mousterian period was 
' See Archcroloi^ia^ 191 ij vol. Ixii. p. 522 ; also G. C. Robson, Trans. 
Oxford University Junior Scientific Club, 1910, June, p. 337. 
