18 GEOGRAPHICAL DISTRIBUTION [CHAP. VII 



Letter 392 plants in relation to your views ; but he seemed to doubt 

 whether he should ever have time. 



And now I have done my jottings, and once again con- 

 gratulate you on having brought out so grand a work. I 

 have been a little disappointed at the review in Nature^ 



Letter 393 A. R. Wallace to C. Darwin. 



Rosehill, Dorking, July 23rd, 1876. 



I should have replied sooner to your last kind and 

 interesting letters, but they reached me in the midst of my 

 packing previous to removal here, and I have only just now 

 got my books and papers in a get-at-able state. 



And first, many thanks for your close observation in 

 detecting the two absurd mistakes in the tabular headings. 



As to the former greater distinction of the North and 

 South American faunas, I think I am right. The edentata 

 being proved (as I hold) to have been mere temporary 

 migrants into North America in the post-Pliocene epoch, 

 form no part of its Tertiary fauna. Yet in South America 

 they were so enormously developed in the Pliocene epoch 

 that we know, if there is any such thing as evolution, etc., 

 that strange ancestral forms must have preceded them in 

 Miocene times. 



Mastodon^ on the other hand, represented by one or two 

 species only, appears to have been a late immigrant into 

 South America from the north. 



The immense development of ungulates (in varied 

 families, genera, and species) in North America during the 

 whole Tertiary epoch is, however, the great feature which 

 assimilates it to Europe, and contrasts it with South America. 

 True camels, hosts of hog-like animals, true rhinoceroses, 

 and hosts of ancestral horses, all bring the North American 

 [fauna] much nearer to the Old World than it is now. 

 Even the horse, represented in all South America by Equus 

 only, was probably a temporary immigrant from the north. 



As to extending too far the principle (yours) of the 

 necessity of comparatively large areas for the development 

 of varied faunas, I may have done so, but I think not. 

 There is, I think, every probability that most islands, etc., 



1 June 22nd, 1876, pp. 165 et seq. 



