CHAPTER VI.
POST-PLIOCENE ALLUVIUM AND CAVE DEPOSITS WITH FLINT IMPLEMENTS.
GENERAL POSITION OF DRIFT WITH EXTINCT MAMMALIA IN VALLEYS—DISCOVERIES OF M. BOUCHER DE PERTHES AT ABBEVILLE—FLINT IMPLEMENTS FOUND ALSO AT ST. ACHEUL, NEAR AMIENS—CURIOSITY AWAKENED BY THE SYSTEMATIC EXPLORATION OF THE BRIXHAM CAVE—FLINT KNIVES IN SAME, WITH BONES OF EXTINCT MAMMALIA—SUPER-POSITION OF DEPOSITS IN THE CAVE—VISITS OF ENGLISH AND FRENCH GEOLOGISTS TO ABBEVILLE AND AMIENS.
Post-pliocene Alluvium containing Flint Implements in the Valley of the Somme.
THROUGHOUT a large part of Europe we find at moderate elevations above the present river-channels, usually at a height of less than forty feet but sometimes much higher, beds of gravel, sand, and loam containing bones of the elephant, rhinoceros, horse, ox, and other quadrupeds, some of extinct, others of living, species, belonging for the most part to the fauna already alluded to in the last chapter as characteristic of the interior of caverns. The greater part of these deposits contain fluviatile shells, and have undoubtedly been accumulated in ancient river-beds. These old channels have long since been dry, the streams which once flowed in them having shifted their position, deepening the valleys, and often widening them on one side.
It has naturally been asked, if man coexisted with the extinct species of the caves, why were his remains and the works of his hands never embedded outside the caves in ancient river-gravel containing the same fossil fauna? Why should it be necessary for the geologist to resort for evidence
