And, if physical science shows that no such Deluge as that described in Genesis could have occurred, geology is equally positive that it never did occur. The drift and boulders which cover a great part of Europe and North America are beyond all doubt glacial, and not diluvial. They are strictly limited by the extension of glaciers and ice-sheets, and of the streams flowing from them. The high-level gravels in which human remains are found in conjunction with those of extinct animals, are the result of the erosion of valleys by rivers. They are not marine, they are interstratified with beds of sand and silt, containing often delicate fluviatile shells, which were deposited when the stream ran tranquilly, as the coarser gravels were when it ran with a stronger torrent. And the gravels of adjacent valleys, even when separated by a low water-shed, are not intermixed, but each composed of the _débris_ of its own system of drainage, by which small rivers like the Somme and the Avon have, in the course of ages, scooped out their present valleys to an extent of more than 100 feet in depth and two miles in width. Masses of loose sand, volcanic ashes, and other incoherent materials of tertiary formation remain on the surface, which must have been swept away by anything resembling a diluvial wave. And, above all, Egypt and other flat countries adjoining the sea, such as the deltas of the Euphrates, the Ganges, and the Mississippi, which must have been submerged by a slight elevation of the sea or subsidence of the land, show by borings, carried in some cases to the depth of 100 feet and upwards, nothing but an accumulation of such tranquil deposits as are now going on, continued for hundreds of centuries, and uninterrupted by anything like a marine or diluvial deposit.