These would save whoever follows you great labour. Occasionally I wished myself to know the authority for certain statements, and whether you or somebody else had originated certain subordinate views. Take the case of a man who had collected largely on some island, for instance St. Helena, and who wished to work out the geographical relations of his collections: he would, I think, feel very blank at not finding in your work precise references to all that had been written on St. Helena. I hope you will not think me a confoundedly disagreeable fellow.
I may mention a capital essay which I received a few months ago from Axel Blytt (392/2. Axel Blytt, "Essay on the Immigration of the Norwegian Flora." Christiania, 1876. See Letter 387.) on the distribution of the plants of Scandinavia; showing the high probability of there having been secular periods alternately wet and dry, and of the important part which they have played in distribution.
I wrote to Forel (392/3. See Letter 388.), who is always at work on ants, and told him your views about the dispersal of the blind coleoptera, and asked him to observe.
I spoke to Hooker about your book, and feel sure that he would like nothing better than to consider the distribution of 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 congratulate you on having brought out so grand a work. I have been a little disappointed at the review in "Nature." (392/4. June 22nd, 1876, pages 165 et seq.)
LETTER 393. A.R. WALLACE TO CHARLES 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., where a varied fauna now exists, have been once more extensive--eg., New Zealand, Madagascar: where there is no such evidence (e.g., Galapagos), the fauna is very restricted.
Lastly, as to want of references: I confess the justice of your criticism; but I am dreadfully unsystematic. It is my first large work involving much of the labour of others. I began with the intention of writing a comparatively short sketch, enlarged it, and added to it bit by bit; remodelled the tables, the headings, and almost everything else, more than once, and got my materials in such confusion that it is a wonder it has not turned out far more crooked and confused than it is. I, no doubt, ought to have given references; but in many cases I found the information so small and scattered, and so much had to be combined and condensed from conflicting authorities, that I hardly knew how to refer to them or where to leave off.