Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/106

 prior to the excavation of the Weald valley, whether of Lower Tertiary age or of some subsequent period) which occur near to, and even on, the chalk escarpment, and are shown in the accompanying map. These, however, clearly could not have supplied the pebbles to the Kennington, Willesboro', and Smeeth gravels, which lie within a separate drainage-area — that of the Stour ; and if we suppose those gravels that are shown in the map as lying within the area of the Medway drainage and containing Tertiary pebbles to have been supplied from this source (straining our imagination, and ignoring, in order to do so, various physical features that conflict with such a direction of supply), we ought for consistency to find Tertiary pebbles in increasing proportions in those gravels of the Medway drainage-area, both higher and lower, which lie nearer and nearer to these scarp beds ; but such is not the case.

While the introduction of these pebbles, and the nature and form of the area of denudation seem to me alike repugnant to any conceivable river-agency acting in the direction of the present streams, the position and mode of occurrence of all the gravels within this part of the Weald appear to me to be just what might be expected from the sequence of events after the Thames gravel which I have in previous papers put forward ; and this sequence I will endeavour here to trace in harmony with the composition and position of such gravels.

I should premise, in order to remove misapprehension, that I have never entertained, and wholly reject, the hypothesis of the escarpments having ever been cliffs, although they appear to me to have formed sea-margins and steep foreshores*. The absence, however, of beds with contemporaneous marine fossils within the Weald, either at the feet of the escarpments or on elevations within the major valley, does not seem to me to be entitled to any weight ; for there is proof, from the envelopment of some two or three miles of it in Boulder-clay, that the escarpment of the Yorkshire Wold existed during the glacial period, and must therefore have been a sea-margin, because, in whatever way this Boulder-clay was formed, no one can deny that the Yorkshire Wold passed under the Glacial sea ; and if the valley below it was filled with, and the Wold covered by, ice when subsiding, they were clear of this when emerging, and underwent great denudation during that process. The features exhibited by sections of mine, Nos. 7 & 8, at p. 402 of the 23rd volume of the Society's Journal, render it difficult to deny that the same thing occurred with respect to the chalk-escarpment of Herts and the lower grounds below it. Nevertheless we do not in either of these cases meet with beds with marine fossils referable to this period of emer-

cannot admit that the absence of beaches at their feet is any argument in the case, because hundreds of steep acclivities in the north of England and in Scotland that could not have been any thing else than cliffs when emerging from the glacial sea, are quite destitute of beaches at their feet. Some of these, such as Gristhorpe cliff in Yorkshire, shown by me and Mr. Rome in section at p. 180 of the 24th volume of the Quarterly Journal, have now become cliffs again, and have the beach at their feet, which they had not when rising out of the glacial sea.
 * While rejecting the hypothesis of scarps being in any way allied to cliffs, I