Page:Natural History Review (1862).djvu/267

252 Fig. 4, gives a section across the valley of the Somme at Abbeville, taken from Mr. Prestwich's first paper. We should get almost the same arrangement and position of the different beds, not only at St. Acheul, but elsewhere along the valley of the Somme, wherever the upper beds have not been removed by subsequent action of the river. Even at St. Valery, at the present mouth of the river, we found a bed of gravel at a considerable height above the level of the sea. This would seem to show that at the period of these high level gravels, the channel was narrower than it is at present, as indeed we know to have been the case even in historical times. So early as 1605 our countryman Verstegan pointed out that the waves and tides were eating away our coasts. Sir C. Lyell gives much information on this subject, and it appears that even as lately as the reign of Queen Elizabeth, the town of Brighton was situated on the site now occupied by the Chain Pier.

Mr. Prestwich has shown that a section, similar to that of the Somme, is presented by the Lark, Waveney, Ouse, &c. while it is well shown also along the banks of the Seine. Probably, indeed, it holds good of most of our rivers, that along the sides of their valleys are patches of old gravels left by the stream at various heights, before they had excavated the channels to their present depth. Mr. Prestwich considers that the beds of sand and gravel can generally be divided into two more or less distinct series, one continuous along the bottom of the valleys and rising little above the water level; the other occurring in detached masses at an elevation of 50 to 200 feet above the valley. Rather, perhaps, these are the two extremes of a series, once continuous, but now almost always presenting some interruption. A more magnified view of the strata at St. Acheul, near Amiens, is shown in Fig. 2. The upper layer of vegetable soil having been removed.

1. A bed of brick earth from four to five feet in thickness, and containing a few angular flints.

2. Below this is a thin layer of angular gravel, one to two feet in thickness.

3. Still lower is a bed of sandy marl, five to six feet thick, with land and fresh water shells, which though very delicate, are in most cases perfect.

4. At the bottom of all, and immediately overlying the chalk, is the bed of subanguar gravel in which the flint implements are found.

In the early Christian period this spot was used as a cemetery: the graves generally descend into the marly sand, and their limits are very distinctlv marked. Fig. 2; an important fact, as showing that the rest of the strata have lain undisturbed for 1500 years. The coffins used were sometimes made of hard chalk, sometimes of wood, in which latter case the nails and clamps only remain, every