The flint implements from the valley of the Somme, which have been of so much interest, and convinced so many sceptical geologists, belong to the early part of this epoch. This valley may be represented by Fig. 3.
Fig. 3.
Section Across the Somme in Picardy.
1. Peat, twenty to thirty feet thick, resting on gravel, a.
2. Lower level gravel, with elephants' bones and flint tools covered with fluviatile loam, twenty to forty feet thick.
3. Upper level gravel, with similar fossils, and overlying loam. In all thirty feet thick.
4. Upland loam without shells, five or six feet thick.
5. Eocene tertiary strata, resting on the chalk in patches.
In explanation of the above it may be well to remark that No. 2 indicates the lower level gravels, and No. 3 the higher ones, which are from eighty to one hundred feet above the river. Of a later date than these is the peat, No. 1, which is from ten to thirty feet in thickness. Underneath the peat is a bed of gravel, a, from three to fourteen feet thick, resting on undisturbed chalk. But between the gravel and the peat is a thin layer of impervious clay. This section of the valley of the Somme is a pretty fair representation of the arrangements of the different beds at Abbeville, Amiens, and and St. Acheul.
In these beds are the records of two drift periods, marked by 2 and 3. The two are separated by a layer of fresh-water deposits, which contains river shells and is sometimes as much as sixteen feet thick. The lower, or gray diluvium, (No. 2), marks the glacial epoch, as distinct from the glaciers of the reindeer epoch. In the lower gravel, lying immediately upon the tertiary formation, were found the flint hatchets, together with the bones of the mammoth and fossil rhinoceros.
In order to understand the deposits still more clearly, the following figure is given.
Fig. 4.
Section of a Gravel-pit at St. Acheul.
1. Vegetable and made soil from two to three feet thick.