More Letters of Charles Darwin, vol 2 | Page 9

I have read only to page 184--my object having been to do as
little as possible while resting. I feel sure that you have laid a broad and
safe foundation for all future work on Distribution. How interesting it
will be to see hereafter plants treated in strict relation to your views;
and then all insects, pulmonate molluscs and fresh-water fishes, in
greater detail than I suppose you have given to these lower animals.
The point which has interested me most, but I do not say the most
valuable point, is your protest against sinking imaginary continents in a
quite reckless manner, as was stated by Forbes, followed, alas, by
Hooker, and caricatured by Wollaston and [Andrew] Murray! By the
way, the main impression that the latter author has left on my mind is
his utter want of all scientific judgment. I have lifted up my voice
against the above view with no avail, but I have no doubt that you will
succeed, owing to your new arguments and the coloured chart. Of a
special value, as it seems to me, is the conclusion that we must
determine the areas, chiefly by the nature of the mammals. When I
worked many years ago on this subject, I doubted much whether the
now-called Palaearctic and Nearctic regions ought to be separated; and
I determined if I made another region that it should be Madagascar. I
have, therefore, been able to appreciate your evidence on these points.
What progress Palaeontology has made during the last twenty years!
but if it advances at the same rate in the future, our views on the
migration and birthplace of the various groups will, I fear, be greatly
altered. I cannot feel quite easy about the Glacial period, and the
extinction of large mammals, but I must hope that you are right. I think
you will have to modify your belief about the difficulty of dispersal of
land molluscs; I was interrupted when beginning to experimentise on

the just hatched young adhering to the feet of ground-roosting birds. I
differ on one other point--viz. in the belief that there must have existed
a Tertiary Antarctic continent, from which various forms radiated to the
southern extremities of our present continents. But I could go on
scribbling forever. You have written, as I believe, a grand and
memorable work, which will last for years as the foundation for all
future treatises on Geographical Distribution.
P.S.--You have paid me the highest conceivable compliment, by what
you say of your work in relation to my chapters on distribution in the
"Origin," and I heartily thank you for it.
LETTER 390. FROM A.R. WALLACE TO CHARLES DARWIN.
The Dell, Grays, Essex, June 7th, 1876.
Many thanks for your very kind letter. So few people will read my
book at all regularly, that a criticism from one who does so will be very
welcome. If, as I suppose, it is only to page 184 of Volume I. that you
have read, you cannot yet quite see my conclusions on the points you
refer to (land molluscs and Antarctic continent). My own conclusion
fluctuated during the progress of the book, and I have, I know,
occasionally used expressions (the relics of earlier ideas) which are not
quite consistent with what I say further on. I am positively against any
Southern continent as uniting South America with Australia or New
Zealand, as you will see at Volume I., pages 398-403, and 459-66. My
general conclusions as to distribution of land mollusca are at Volume
II., pages 522-9. (390/1. "Geographical Distribution" II., pages 524,
525. Mr. Wallace points out that "hardly a small island on the globe but
has some land-shells peculiar to it"--and he goes so far as to say that
probably air-breathing mollusca have been chiefly distributed by air- or
water-carriage, rather than by voluntary dispersal on the land.) When
you have read these passages, and looked at the general facts which
lead to them, I shall be glad to hear if you still differ from me.
Though, of course, present results as to the origin and migrations of
genera of mammals will have to be modified owing to new discoveries,
I cannot help thinking that much will remain unaffected, because in all
geographical and geological discoveries the great outlines are soon
reached, the details alone remain to be modified. I also think much of
the geological evidence is now so accordant with, and explanatory of,
Geographical Distribution, that it is prima facie correct in outline.

Nevertheless, such vast masses of new facts will come out in the next
few years that I quite dread the labour of incorporating them in a new
edition.
I hope your health is improved; and when, quite at your leisure, you
have waded through my book, I trust you