Page:Popular Science Monthly Volume 12.djvu/74

64 valley-gravels. They are found mixed through them, or more commonly at their base. Palæolithic implements are found in the same position, though usually in gravel higher up on the slopes of the valleys. When found in the gravel, the bones are broken and worn, and the flint implements have their angles rounded more or less as if by rolling. When, as has happened in a few cases, the bones and implements have been found below the gravels, they have been uninjured and unworn. Mr. Godwin Austen noticed the occurrence of bones of the mammoth in an old forest-bed beneath the valley-gravels, at Pease marsh, in Surrey, uninjured and lying together, while in the overlying gravel the teeth of the mammoth were found singly and rolled. And Colonel Lane Fox has recorded the discovery of flint implements at Acton in seams of white sand, nine feet from the surface, beneath deposits of gravel and brick-earth. Their edges were as sharp as if just flaked off a core of flint; while those found in the gravel, on the contrary, have their edges worn and rounded just like those of the subangular pebbles of which the gravel is principally composed.

The position and the state of preservation of the bones and implements are such as might be expected if they had been deposited on an old land-surface before the outspread of the gravels, when the configuration of the country was much the same as now; and I have suggested that the occurrence of the implements, generally higher up the slopes of the valleys than the mammalian remains, is due to palæolithic man having frequented more elevated and drier localities than the great mammals. I have urged that the outspread of the gravels was due, as formerly supposed by Sedgewick, De la Beche, and Murchison, to the action of a great flood or debacle. I have advanced the theory that that debacle was caused by the breaking away of a barrier of ice that blocked up the English Channel, and with it nil the drainage of Northern Europe, causing an immense lake of fresh or brackish water that was thus suddenly and tumultuously discharged.

This great flood occurred, according to my theory, before the culmination of the Glacial period, and was primarily due to ice filling the bed of the North Atlantic as far south on the European side as latitude 49°. If the gravels in and below which the rude flint implements and the remains of the extinct mammals are found, were thus spread out, it follows that they were preglacial in the sense that they lived before the principal glaciation of the country.

We have seen that, in the north, such an excellent geologist as the late Prof. Phillips had arrived at this conclusion with regard to the age of the mammoth, the woolly rhinoceros, and the