WCP4979

[1]¹ [p. 334]

Waldron Edge, Duppas Hill, Croydon,

10^th August 1879.

James Croll, Esq.

My dear Sir,—Your kind letter was very welcome to me, especially as it also conveys to me Mr. James Geikie's approval of my article. Well knowing my want of practical acquaintance with the phenomena of glaciation, I feel that it is presumptuous in me to write judicially on so complex a subject. My excuse is that for many years the question has been one of the intensest interest to me, and I have taken every opportunity of studying the chief writings bearing upon it. I can only hope that I have fallen into no serious errors [2] [p. 335] or misstatements such as dabblers in subjects that don't belong to them are always liable to. I shall take it as a favour if you will point out without hesitation any statements, whether of fact or of theory, that you think require correction, as the chief part of the article will be embodied in a chapter of a work I am now preparing on the causes which have affected the dispersal of animals.

Perhaps you can ascertain from some of the Edinburgh meteorologists whether there are any connected observations of the amount of solar radiation on or near the equator, so as to show how far the difference of the sun's distance at perihelion and aphelion makes itself apparent. It appears to have no effect on the temperature of the atmosphere, but it certainly ought on the direct radiation, and it would be a most important guide to know what effect it really has. I am a great admirer of the late Mr. Belt's writings, and long held to his view as to the causes of glaciation, but on fuller consideration gave them up. I am still, however, greatly fascinated by his theory of the blocking up of the drainage of continents by ice to explain the wide spread of loess and gravel. The ordinary explanations seem utterly inadequate if the facts stated in Belt's papers are anywhere near true. I can hardly accept, however, the mid-Atlantic glacier from Greenland to the Bay of Biscay. Might it not be possible that the confluent glacier of Norway, Scotland, Ireland, and Wales blocked up the North Sea and English Channel? This, with some elevation of the land and some lowering of the ocean, might give almost as much "damming up" as seems needful in Europe.—Believe me, yours very faithfully,

Alfred R. Wallace.