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wiuter, the melting of the snows turned it every spring 
into a roaring torrent. These floods were probably more 
destructive to animals even than man himself ; while, how- 
ever rude they may have been, our predecessors can hardly 
be supposed to have been incapable of foreseeing and 
consequently escaping the danger. While the water at 
an elevation of 150 feet above its present level, as for 
instance at Liercourt, had sufficient force to deposit coarse 
gravel ; at a still higher level it would part with finer 
particles, and would thus form the loess which, at the 
same time, would here and there receive angular flints 
and shells brought down from the hills in a more or less 
transverse direction by the rivulets after heavy rains. 
At length the excavation of the valley was completed ; 
the climate must have approached what it is now, and 
whether from this change, or whether perhaps yielding to 
the irresistible power of man, the great Pachydermata had 
become extinct. Under new conditions, the river, unable 
to carry out to sea the finer particles brought down from 
the higher levels, deposited them in the valley, and thus 
raised somewhat its general level, checking the velocity 
of the stream, and producing extensive marshes, in which 
a thick deposit of peat was gradually formed. We have, 
unfortunately, no reliable estimate as to the rate of formation 
of this substance, but on any supposition the production of 
a mass more than 20 feet in thickness must have required 
a very considerable period. Yet it is in these beds that we 
find the remains of the stone period. From the tombs at 
St. Acheul, from the Eoman remains found in the peat 
near the surface of the ground, at about the present level 
of the river, we know that fifteen hundred years have 
produced scarcely any change in the configuration of the 
valley. In the peat, and at a depth of about 15 feet in the 
alluvium at Abbeville, are the remains of the stone period, 
