MEN OF THE loo-FOOT TERRACE 165 
tion, or, more probably, a re-excavation of the valley 
almost to its present depth. At Swanscombe the 
magnitude of such an operation is apparent, for the 
corresponding (100-foot) terrace on the opposite or 
north side of the valley lies eight to ten miles distant. 
The whole width of the valley was apparently cut down to 
an extent of 100 feet during the later part of the Acheulean 
period. It does not matter for our present argument 
whether the Thames cut her valley for the first time, or 
whether, as seems more probable, she only cleared out 
a former channel which had become silted up during a 
former period of submergence. It is clear, when we 
consider the magnitude of the operations involved, that 
the Acheulean culture covers a long period of time, one 
more than equal to all the later Palaeolithic periods put 
together — Mousterian, late Palaeolithic, Neolithic, and 
Metal phases of human culture. If we pitch the com- 
mencement of the Mousterian period, as a provisional 
hypothesis, at a distance of fifty thousand years, we must 
give fifty thousand years more to reach the opening 
phases of the Acheulean period. 
Considering the great duration of the Acheulean 
period, and the abundant evidence of the activity and 
culture of the men of that time, it is surprising that so 
little has been discovered of the men themselves. In 
nearly every case where remains of man have been 
ascribed to the Acheulean period, the authenticity of the 
discovery has been questioned or denied. The very first 
instance I am to cite is one which is placed — and rightly 
placed so — to what the geologist calls a " suspense " 
account. Those suspense cases often prove the most 
instructive. Such cases should not be allowed to pass 
into oblivion ; the facts ought to be placed on record, to 
await the fate which will be assigned to them in the light 
of discoveries made at a future date. The suspense 
cases may prove false or prove true. They stimulate 
further research. The first discovery I am to mention 
brought to light the " Dartford " skull — supposed to be 
of Acheulean date. Dartford, as may be seen from 
