WCP2475

[1]

UNIVERSITY OF EDINBURGH

24^th Oct. 1983

Dear Sir

I have read your article¹ with the liveliest interest. Your argument as to the subaqueous contours ^{& superficial outlines} of the lake basin is, so far as I know, quite original, and is certainly most convincing. I don’t see how the opponents of glacial erosion can wriggle out of it!

I am not so sure of the old "alluvium" underneath the glacial deposits never Geneva being a preglacial age. The "alluvium" consists chiefly of gravel & shingle, and seem to me to be of the same character and origin of as the gravels which underlay the boulder clay and morraines opposite the newer ends of all the great Alpine Lakes. They are the gravels which were swept out from underneath the advancing glaciers, and are thus of flurio-glacial origin. It [2] is improbable. I think that any preglacial alluvium could have been preserved in such positions. The glacial deposits that overlie the particular alluvium in question are those belonging to the latest great advance of the glaciers. Even if it could be shown that the glacial deposits referred to really pertain to the earlier epoch of greatest glacier extension — still that would not show that the underlying alluvial gravels were of preglacial age and therefore ordinary river accumulation. Gravels have always opened out in advance of the glaciers. Thus when a glacier came to occupy the basin of Lake Geneva, gravels, swept out from the mass, would be distributed over the low grounds in front of the ice.

This, however is a relatively small point and does not weather in any way your general arguments.

[3] I was much obliged to you for your former letter in which you remark upon the thickness of the Palaeozoic deposits being taken on evidence by the extent of depression of the land. Of course I don’t maintain that a thickness of 10,000 or 20,000 feet of shallow water beds indicate gradual depression to that extent. Doubtless some sediments were laid down in shallow water, and finer sediments accumulated contemporanously in deeper water. But I doubt whether the condition in Palaeozoic times were on all [illeg.] with what we now. The earlier Palaeozoic strata afford no evidence whatever of deep water conditions — nothing comparable to what we have now. — Unless we take the radio[illeg.] chart beds recently discovered in our Lower Silurian in Southend as evidence of deep-sea conditions. It is the enormous areas occupied by the older Palaeozoic strata and the forest thickness which they retain over wide regions that incline one to believe that [4] they have been accumulated over in shallow seas upon a gradually sinking floor. But enough!

I see you refer in your papers to Shetlands estimate in to the glacial erosion of Scandinavia. I could give you several similar estimates made by Penck, Böhm & others as to the glacial erosion of the alps. But the one you cite is probably sufficient for your purpose.

Believe me | yours very truly | James Geikie² [signature]

Kind regards to my Cousin³ when next you see him.

[5] PS. There is another point in your paper trust you will excuse me if I refer to,

On page 9 you say that there is no reason why loose accumulation underneath a glacier should be eroded. It is quite true that they would not be ground down & absorbed as if they were hard rock. But we have evidence to show that loose materials were [illeg.] pushed and dragged forward underneath ice. Thus in some places one sees beds of gravel, sand & clay thrown into the wildest confusion—con contorted, plicated, —and the boulder-clay forced into them: Again, one may [sketch depicting the above] note how considerable thickness of these incoherent deposits have been dragged out of place and gradually incorporated with the ground morraine. Great sheets of Tertiary beds (Brown Coral beds) in N. Germany have been forcibly dragged [5] foward and become enclosed in Till & the like has happened with the Chalk. The Even in the Alpine ground morraines one sees enormous block (which could ^only not level come from the bed of the glacier), so that one is compelled to believe that glaciers not only grind and abrade but crush, dislocate & displace rocks. The recurrence of undisturbed ground etc. underneath the terminal points of a glacier is as everyone knows common enough. But towards its terminal end the ice owing to its diminished thickness and a much diminished rate of flow has ceased either to erode or drag. All this you know quite well, but if some reference be not made to it, some one will be sure to call attention to it—and it is better perhaps to forestall him!