Page:A Treatise on Geology, volume 1.djvu/334

 318 and the violent currents which distributed, the diluvium. Nor would the ordinary currents of the sea be adequate to the effect. It is requisite further to conceive that the sea was most violently disturbed, either over the points whence the detritus was brought (which supposes those points also to have been under the waves), or at some other situation. In the latter case, we may, perhaps, imagine so great a violence of water to be generated, as to permit the waves to be thrown to some height over the land; and it seems not impossible hereafter, when the geographical relations of the diluvium are well understood, to offer some reasonable explanation of the whole matter, on the principle now known to be true, of great and sudden changes of relative level of land and sea, which, though limited in the area of the masses moved, might have very extended effects through the agency of water. Floating glaciers may also be called to aid the speculation; but they would be useless for any other purpose than to explain particular cases of erratic blocks, and small tracts of peculiarly associated gravel masses.

The best general view of these phenomena recognises in the greater portion of the materials of these deposits the spoils of neighbouring or not far distant land, derived from the sudden ruin of sea cliffs and the gradual waste occasioned by atmospheric action and river erosion. These materials are sorted into gravel beds, sand beds, and broad masses of clay. In addition, we have considerable quantities of far travelled rock masses, often quite unworn, which are so mixed with the fine clay as to indicate the probability that they were not drifted with it by excessive violence of water, but thrown into it, and inextricably mixed with it by a distant operation, the melting or overturning of stone-covered icebergs. Similar stones, but worn and rounded, occur in the gravels, and no doubt have often been washed out of their original sites in the boulder clay. Perhaps it