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 northwest 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-
