Page:The Ancient Stone Implements (1897).djvu/692

670 during its period of flood. When once they had been thus left, the chances of their being again assailed by the stream would become more and more remote with each successive flood; and though the waters might reach some deposit of the larger pebbles formerly carried down by the main stream, but now at a distance from it, yet they would only belong to the more sluggish portions of the flood, and at first might envelope them in beds of sand; and subsequently, when they were only accessible to the more stagnant turbid waters, leave layer upon layer of muddy silt or clay upon them. In forming the more loess-like beds the action of the wind in transporting sand and dust might also assist. In some cases, and especially at the extremity of curves, and at the end of the tongue between two streams, the accumulation of one period, though at a lower level than that of earlier date, might abut upon it, or even become mingled with it, so that an almost continuous coating of Drift-deposits might extend from the highest level to the lowest.

The bulk, however, of the deposits of one inundation would be moved by the next, or by one of those which subsequently recurred; and stones, and pebbles, and other objects might thus be transported down stream, from place to place, an indefinite number of times, and form constituent parts of an indefinite number of gravelly beds along the bottom of the flooded stream. They might, under some circumstances, lie for a long period of years in some particular bed, in which they would become stained by salts of iron or otherwise, and subsequently be transported and re-deposited among unstained, or differently stained pebbles. The angles of any flints thus transported from place to place would also become rolled, as would, in like manner, those of bones or teeth. In the same way, assuming, as we have done, that the surface of the Chalk in the district was in part, or wholly, covered with beds of marine clay and shingle, it is evident that in the earlier deposits, when the river flowed at the higher level, and was, as it were, commencing to excavate its valley, the proportion of the pebbles derived from these beds to the flints washed out from the Chalk, would be much greater than at a later period. For in the course of time the river would have worked its way below the level of these upper beds, and many of the pebbles at first deposited in its gravels would have been disturbed, again and again, in their beds; on each disturbance carried farther down the stream, and eventually so far as the sea or the tidal portion of the river. At the same time the