WCP2217

[1]

73 Harley St

Feby 2 1869

Dear Wallace

The more I think over what you said yesterday about the Geographical distribution of tropical animals & plants in the Glacial Period, the more I am convinced that Darwin’s¹ difficulty may be removed by duly attending to the effects of the absence of cold. The intensity of heat whether in the sea or in the air is not so important as ^{you remarked as} uniformity of Temperature.

It is universally known that in the Mediterranean coast flora palms & some [2] other African forms creep round low lands near the shore even to the foot of the Maritime Alps. It may therefore be proved that in the Glacial Period there was a migration of North Temperate forms along the Andes from the northern to the Southern Hemisphere, and yet at the base of such a chain tropical plants & insects & mammalia may have flourished.

It is for those who maintain the violent contrast of the climate of the two Hemispheres in the Glacial Period, to show us Qquaternary or Post Pliocene deposits oc= [3] cupying a position 25° north & south of the Equator full of types proper to our temperate region & with such an absence of tropical forms as could imply that these had been annihilated even at a moderate height above the level of the sea. I know of no evidence of this kind, and I don’t think that Darwin has given any time or thought to Croll’s² eccentricity theory³ or to my chapters upon it, and I wish much that he could see your review⁴ before he came out with this new edition of "The Origin".⁵ For I am afraid [4] that he will make too much of the supposed corroboration afforded by the imaginary warmth of the Southern Hemisphere, of the equally hypothetical expulsion of tropical forms from the Equatorial zone north of the line.

ever truly yrs | Cha Lyell⁶ [signature]

A. Wallace Esq—