WCP4123

[1]

Parkstone, Dorset.

May 12th. 1893

Dear Prof. Geikie¹

Many thanks for your interesting letter.² I have a friend here who is a fellow of the Geol. Soc. (Captⁿ. Marshall Hall),³ & he will get me any books from their library. I am sorry I do not read German, so must be content with what I can get from English & French authors.

I am glad you still uphold the glacier-erosion theory, as it certainly seems to me very satisfactory. Most of the objections [2] are very weak,— such as those which object that there are no lakes where there ought to be if ice produced them. They forget that there must be differential erosion to produce a lake— Uniform erosion will only deepen a valley.

Another point is, that there must have been still ice at the bottom of some valley, where the exit is a narrow gorge. I presume in the valleys above the "via mala", and the gorge of Pfeffers⁴ the ice must have been almost or quite stationary at the bottom [3] and have sheared at a level above the narrow cleft. Has that point ever been discussed? Might not even the comparatively wide gorge of the Rhone below Martigny, together with the abrupt bend there, have dammed the ice above so that there was little erosive power on the valley floor, & thus no lakes? This has been suggested as explaining why there are no lakes in the Acosta valley — Many points of this kind need discussions, yet the objectors seems to think that if one lake is formed by ice lakes sh^d. necessarily be formed in every valley where [4] the ice was equally thick.

I will get Clifton Ward⁵ papers^6,7 and the 2nd. Ed. of your "Great Ice Age".⁸

Yours very faithfully | Alfred R. Wallace. [signature]