266 ORIGINAL AKTICLES. 



" present a succession of salient and retiring angles." (Lyell, Princi- 

 ples, p. 206.) During these wanderings from one side of the 

 valley to the other, the river continually undermines, and removes 

 the gravels which at an earlier period it had deposited. Thus the 

 upper-level gravels are now only to be found here and there, as it 

 were in patches, while in many parts they have altogether disappeared, 

 as, for instance, on the right side of the valley between Amiens and 

 Pont Eemy, where hardly a trace of the high level gravels is to be 

 seen. 



At length the excavation of the valley was completed ; the cli- 

 mate must have aj)proached what it is now, and whether from this 

 change, or whether pei'haps 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 genei'al level, checking the velocity of the stream, 

 and producing extensive marshes, in which a thick deposit of peat 

 was gradually formed. "We have, unfoi'tunately, no reliable estimate 

 as to the rate of formation of this svibstauce, but on any supposition 

 the production of a mass more than 20 feet in thickness must have 

 acquired a very considerable period. Yet it is in these beds that we 

 find the remains of the stone period. Prom 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,* which we 

 know from the researches in Denmark and Switzerland to be of an 

 age so great that it can only be expressed in thousands of years. 

 Yet all these are subsequent to the excavation of the valley ; what 

 antiquity then are we to ascribe to the men who lived when the 

 Somme was but beginning its great taslc ? No one can properly ap- 

 preciate the time requu'ed who has not stood on the heights of Lier- 

 court, Picquigny, or on one of the other points overlooking the valley : 

 nor, I am sure, could any geologist return from such a visit without an 

 overpowering sense of the change which has taken place, and the enor- 

 mous time which must have elapsed since the first appearance of man 

 in Western Europe. 



* We shall probably ere long be able to divide this era into several divisions. 

 Already we have two well marked epochs, the elephantine and the post-elephantine. 

 But Prof. Worsaac proposes, and not withont reason, to subdivide this latter into the 

 period of the " Kjdkkenmijddings " on the one hand, and that of the " Pfalilbautcn " 

 on tlie other. The contents of the Danish tumuli belonging to the Stone period, 

 agree ratlicr with tliose from the lake habitations of Switzerland, than with those 

 which occur in tlic Refuse-heaps of Denmark, and though we could not expect to 

 find numy well-worked implements in the kjokkenmoddings, we ought otherwise 

 surely to have obtained ere now at least some broken pieces of the beautiful Hint 

 weapons which were so common in Denmark during the later part of the stone period. 



