354 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 15, 



the probability of a fresh -water origin. The highly water-rolled 

 complexion of the pebbles, again, is also in favour of this view. And 

 then, as to the immense profusion of this gravel being apparently 

 beyond the power of such streams as now occupy the valleys, this is 

 a difficulty that vanishes greatly on consideration; for it is a mere 

 question of time. A stream flowing through stony drift will in a 

 given time produce a certain amount of gravel; give it long enough, 

 and what will it not accomplish ? During the long array of centu- 

 ries, when the bed of the Pleistocene sea was heaving up a broader 

 and broader horizon, the rivers, big and swollen, wandered onward, 

 bearing to the ocean the rain and snow of countless winters. Their 

 basins filled with drift, they must have flowed along at heights far 

 above where we now see them, shifting their channels unchecked by 

 the hand of man, until they gradually wore them down, deeper and 

 deeper, into their present grooves. Give them an infinity of time, 

 and could they not spread out an infinity of gravel ? 



It is probable, therefore, that the rivers have had much to do with 

 the formation of these beds ; but still there are some features in con- 

 nexion with them that river-action alone will scarcely account for. I do 

 not see, for instance, how any river could so thoroughly scour out the 

 drift as has been done in the narrower parts of most of the valleys 

 and even in many of their wider portions, leaving in trough-shaped 

 hollows not a trace of shingle or debris, and this in localities where, 

 as I shall afterwards show, the mass of drift must have been immense, 

 even some hundreds of feet deep. It may, however, be here objected 

 that this clearing out of the drift has been the result of a later set 

 of glaciers moving down the valleys after the period of the marine 

 drift, and ploughing through that deposit. But had this been so, would 

 not the glacier have pushed the drift before it in a rapidly accumula- 

 ting hill, or thrown it on either side as is done by a snow-plough? In 

 the one case we should expect to find some traces of these gigantic 

 terminal moraines, — in the other, some relics of equally extensive 

 lateral ones, — neither of which have I met with in those valleys I 

 have examined. Further, if a glacier had thus ploughed through the 

 drift, it would have left a ready-made groove for the rivers, so that 

 we should not expect to find this gravel at the heights of 200 or 

 300 feet above the beds of the streams, as we often see it. Never- 

 theless I do not mean to deny the existence of glaciers after tbe 

 marine drift, but only to say that I have not hitherto met with any 

 satisfactory proof of their presence at this later period in the lower 

 parts of our larger river-valleys, although, as will be subsequently 

 shown, I do think there are grounds for suspecting their agency in 

 such localities previous to the marine drift. 



At all events there seems to be no trace of glacier- debris above 

 this gravel; so that its origin is likely to have been subsequent to all 

 such action, at any rate in the lower grounds. 



Other objections which forcibly urge themselves against the supposi- 

 tion of the present arrangement of this surface -gravel being entirely 

 due to river-action arise from the fact of its being occasionally piled 

 up in great undulating mounds and tumuli 40 to 100 feet high, 



