CHAP. vin. LOWER-LEVEL GRAVELS OF THE SOMME VALLEY. 121 



CHAPTER VIII. 



POST-PLIOCENE ALLUVIUM WITH FLINT IMPLEMENTS OF THE 

 VALLEY OF THE SOMME, 



Concluded. 



FLUVIO-MARINE STRATA, WITH FLINT IMPLEMENTS, NEAR ABBEVILLE 



MARINE SHELLS IN SAME CYRENA FLUMINALIS MAMMALIA 



ENTIRE SKELETON OF RHINOCEROS FLINT IMPLEMENTS, WHY FOUND 



LOW DOWN IN FLUVIATILE DEPOSITS RIVERS SHIFTING THEIR 



CHANNELS RELATIVE AGES OF HIGHER AND LOWER-LEVEL GRAVELS 



SECTION OF ALLUVIUM OF ST. ACHEUL TWO SPECIES OF ELEPHANT 



AND HIPPOPOTAMUS COEXISTING WITH MAN IN FRANCE VOLUME OF 



DRIFT, PROVING ANTIQUITY OF FLINT IMPLEMENTS ABSENCE OF 



HUMAN BONES IN TOOL-BEARING ALLUVIUM, HOW EXPLAINED VALUE 



OF CERTAIN KINDS OF NEGATIVE EVIDENCE TESTED THEREBY 



HUMAN BONES NOT FOUND IN DRAINED LAKE OF HAARLEM. 



IN the section of the valley of the Somme, given at p. 106 

 (fig. 7), the successive formations newer than the chalk 

 are numbered in chronological order, beginning with the 

 most modern, or the peat, which is marked No. 1, and 

 which has been treated of in the last chapter. Next in the 

 order of antiquity are the lower-level gravels No. 2, which we 

 have now to describe; after which the alluvium, No. 3, found 

 at higher levels, or about eighty and one hundred feet above 

 the river-plain, will remain to be considered. 



I have selected, as illustrating the old alluvium of the 

 Somme occurring at levels slightly elevated above the present 

 river, the sand and gravel-pits of Menchecourt, in the north 

 west suburbs of Abbeville, to which, as before stated, p. 94, 

 attention was first drawn by M. Boucher de Perthes, in his 

 work on Celtic antiquities. Here, although in every adjoin- 



