In the valley of the Somme the chronological data relating to the Glacial period, and indicating a great antiquity for man, have been thought to be more distinct than anywhere else in Europe. As already stated, it is the prevalent opinion that since man first entered the valley, in connection with the mammoth and the other extinct animals characteristic of the Glacial period, the trough of the Somme, about a mile in width and a hundred feet in depth, has been eroded by the drainage of its present valley. An extensive accumulation of peat also has taken place along the bottom of the trough of the river since it was originally eroded to its present level. This substance occurs all along the bottom of the valley from far above Amiens to the sea, and is in some places more than thirty feet in depth. The animal and vegetable remains in it all belong to species now inhabiting Europe. The depth of the peat indicates that when it was formed the land stood at a slightly higher elevation than now, for the base of the stratum is now below the sea-level, while the peat is of fresh-water origin, and, according to Dr. Andrews,[EP] is formed from the vegetable accumulations connected with forest growths. When, therefore, the country was covered with forests, as it was in prehistoric times, the accumulation must have proceeded with considerable rapidity. This inference is confirmed by the occurrence in the peat of prostrate trunks of oak, four feet in diameter, so sound that they were manufactured into furniture. The stumps of trees, especially of the birch and alder, were also found in considerable number, standing erect where they grew, sometimes to a height of three feet. Now, as Dr. Andrews well remarks, it is evident that, in order to prevent these stumps and prostrate trunks from complete decay, the accumulation of peat must have been rapid. From certain Roman remains found six feet and more beneath the surface, he estimates that the accumulation since the Roman occupation has been as much as six inches a century, at which rate the whole would take place in somewhat over 5,000 years. [Footnote EP: American Journal of Science, October, 1868.] Still, if we accept this estimate, we have obtained but a starting-point from which to estimate the age of the high-level gravels in which palæolithic implements were found; for, if we accept the ordinary theory, we must add to this the time required for the river to lower its bed from eighty to a hundred feet, and to carry out to the sea the contents of its wide trough. But, as already shown, the Glacial period was, even in the north of France, a time of great precipitation and of a considerable degree of cold, when ice formed to a much greater extent than now upon the surface of the Somme. The direct evidence of this consists in the boulders mingled with the high-level gravel which are of such size as to require floating ice for their transportation.