Page:Natural History Review (1862).djvu/278

Rh of the river, and gradual excavation of the valley, which, by supplying the floods with a lower bed, left the waters at this height with a gradually diminishing force and velocity.

The upper part of the section at St. Acheul consists of brick earth, passing below into angular gravel, while between this and the underlying sandy marl is sometimes a small layer of darker brick earth. These beds, however, vary much even in adjoining sections. Taken as a whole they are regarded by Mr. Prestwich as the representatives of that remarkable loamy deposit which is found overlying the gravels in all these valleys of Northern Prance, and which, as the celebrated "loëss" of the Rhine, attains a thickness of 800 feet. The greatest development of it which I have seen was in a pit in the Rue de la Chevalerie, near Ivry, where it was twenty-two feet thick, some of which however may have been reconstructed loëss brought down by rain from the higher ground in the immediate neighbourhood.

Assuming that this loëss is composed of fine particles deposited from standing or slowly moving waters, we might be disposed to wonder at not finding in it any traces of vegetable remains. We know, however, from the arrangement of the nails and hasps that in some of the St. Aeheul tombs wooden coffins were used, while the size of the nails shows that the planks must have been tolerably thick; yet in these cases every trace of wood has been removed, and not even a stain is left to indicate its presence.

Such is a general account of those gravel pits which lie at a height of from 80 to 150 feet above the present water level of the valleys, and which along the Somme are found in some places even at a height of 200 feet.

Let us now visit some of the pits at the lower levels. At about thirty feet lower, as for instance at Menchecourt, near Abbeville, and at St. Roch, near Amiens, where the gravels slope from a height of about sixty feet down to the valley, we find almost a repetition of the same succession; coarse subangular gravel below, finer materials above. So similar, indeed, are these beds to those already described, both in constitution and in the animal remains they contain, that it will be unnecessary for me to give any farther description of them.

Finally, the lowest portion of the valley is at present occupied by a bed of gravel, covered by silt and peat, which latter is in some places more than twenty feet thick, and is extensively worked for fuel. These strata have afforded to the antiquaries of the neighbourhood, and especially to M. Boucher de Perthes, a rich harvest of interesting relics belonging to various periods. The depth at which these objects are found has been carefully noted by M. Boucher de Perthes.

"Prenant" he says, "pour terme moyen du sol de la vallée, une hauteur de 2 mètres audessus du niveau de la Somme, c'est à 30 à 40 centimètres de la surface qu'on rencontre le plus abondamment