But a river which is thus digging down its channel in one place, deposits the materials so dug away at other and lower levels, as beds of sand and gravel. In the course of time, as the river gradually lowers its channel, it will leave behind, at varying heights along its banks, scattered patches of such beds. Wherever we find them, no matter how far removed, or how high above the present river, we are sure that at some time the river flowed at that height; and standing there, we may try and imagine how different the country must have looked before the present deep valley was eroded. In the case of the river Somme, we have a wide and deep valley, a large part of which has been excavated in chalk rock, through which the river now winds its way in a sinuous course to the English Channel. Yet we feel sure that at some time in the past it was a mighty stream, and that its waters surged along over a bed at least two hundred feet higher than now. In proof of this fact we still find, at different places along the chalky bluff, stretches of old gravel banks, laid down there by the river, “reaching sometimes as high as two hundred feet above the present water level, although their usual elevation does not exceed forty feet.”32 The history of the investigation of the ancient gravel beds of the Somme is briefly this: More than one instance had been noted of the finding of flint implements, apparently the work of men, in association with bones of various animals, such as hyenas, mammoths, musk-sheep, and others, which, as we have just seen, lived in Europe during the Glacial Age. In a number of cases such finds had been made in caves. But for a long time no one attributed any especial value to these discoveries, and various were the explanations given to account for such commingling. A French geologist, by the name of Boucher DePerthes, had noted the occurrence of similar flint implements, and bones of these extinct animals, in a gravel pit on the banks of the Somme, near Abbeville, France. He was convinced that they proved the existence of man at the time these ancient animals lived in Europe. But no one paid any attention to his opinions on this subject, and a collection of these implements, which he took to Paris in 1839, was scarcely noticed by the scientific world. They were certainly very rude, and presented but indistinct traces of chipping, and perhaps it is not strange that he failed to convince any one of their importance. He therefore determined to make a thorough and systematic exploration of these beds at Abbeville. In 1847 he published his great work on this subject, giving over sixteen hundred cuts of the various articles he had