Alfred Russel Wallace 



Yet, because there has been continuity, the difficulty is 

 slurred over or thought to be explained ! — ^Yours very truly, 



Alfred R. Wallace. 



To Sir W. T. Thiselton-Dybr 

 Old Orchard, Broadstone, Wimborne. June 22, 1909. 



Dear Sir William, — On Saturday, to my great pleasure, 

 I received a copy of the Darwin Commemoration volume. 

 I at once began reading your most excellent paper on the 

 Geographical Distribution of Plants. It is intensely in- 

 teresting to me, both because it so clearly brings out 

 Darwin's views and so judiciously expounds his arguments 

 — even when you intimate a difference of opinion — but 

 especially because you bring out so clearly and strongly 

 his view^s on the general permanence of continents and 

 oceans, which to-day, as much as ever, wants insisting 

 upon. I may just mention here that none of the people 

 who still insist on former continents where now are deep 

 oceans have ever dealt with the almost physical impossi- 

 bility of such a change having occurred without breaking 

 the continuity of terrestrial life, owing to the mean depth 

 of the ocean being at least six times the mean height of 

 the land, and its area nearly three times, so that the whole 

 mass of the land of the existing continents would be re- 

 quired to build up even one small continent in the depths 

 of the Atlantic or Pacific! I have demonstrated this, with 

 a diagram, in my " Darwinism " (Chap. XII.), and it has 

 never been either refuted or noticed, but passed by as if it 

 did not exist ! Your whole discussion of Dispersal and Dis- 

 tribution is also admirable, and I was much interested with 

 your quotations from Guppy, whose book I have not seen, 

 but must read. 



Most valuable to me also are your numerous refer- 

 ences to Darwin's letters, so that th^ article serves as a 



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