lately exhibited was four thousand years old, so that one
individual might see a chain of hills rise, and rise with it, much
[more] a species--and those islands which J. Hooker describes as covered
with New Zealand plants three hundred (?) miles to the N.E. (?) of New
Zealand may have been separated from the mainland two or three or four
generations of Washingtonia ago.

If the identity of the land-shells of all the hundreds of British Isles
be owing to their having been united since the Glacial period, and the
discordance, almost total, of the shells of Porto Santo and Madeira be
owing to their having been separated [during] all the newer and possibly
older Pliocene periods, then it gives us a conception of time which will
aid you much in your conversion of species, if immensity of time will do
all you require; for the Glacial period is thus shown, as we might have
anticipated, to be contemptible in duration or in distance from us,
as compared to the older Pliocene, let alone the Miocene, when our
contemporary species were, though in a minority, already beginning to
flourish.

The littoral shells, according to MacAndrew, imply that Madeira and the
Canaries were once joined to the mainland of Europe or Africa, but that
those isles were disjoined so long ago that most of the species came
in since. In short, the marine shells tell the same story as the land
shells. Why do the plants of Porto Santo and Madeira agree so nearly?
And why do the shells which are the same as European or African species
remain quite unaltered, like the Crag species, which returned unchanged
to the British seas after being expelled from them by glacial cold,
when two millions (?) of years had elapsed, and after such migration to
milder seas? Be so good as to explain all this in your next letter.

LETTER 48. TO J.D. HOOKER. Down, July 5th [1856].

I write this morning in great tribulation about Tristan d'Acunha. (48/1.
See "Flora Antarctica," page 216. Though Tristan d'Acunha is "only 1,000
miles distant from the Cape of Good Hope, and 3,000 from the Strait of
Magalhaens, the botany of this island is far more intimately allied to
that of Fuegia than Africa.") The more I reflect on your Antarctic flora
the more I am astounded. You give all the facts so clearly and fully,
that it is impossible to help speculating on the subject; but it drives
me to despair, for I cannot gulp down your continent; and not being able
to do so gives, in my eyes, t