f the Glacial epoch.' What
does Austen make the date of the Channel?--ante or post Glacial?" The
changes in level and other questions are dealt with in a paper by R.A.C.
Austen (afterwards Godwin-Austen), "On the Superficial Accumulations
of the Coasts of the English Channel and the Changes they indicate."
"Quart. Journ. Geol. Soc." VII., 1851, page 118. Obit. notice by Prof.
Bonney in the "Proc. Geol. Soc." XLI., page 37, 1885.)

Down, August 3rd [1866].

I will take your letter seriatim. There is good evidence that S.E.
England was dry land during the Glacial period. I forget what Austen
says, but Mammals prove, I think, that England has been united to the
Continent since the Glacial period. I don't see your difficulty about
what I say on the breaking of an isthmus: if Panama was broken through
would not the fauna of the Pacific flow into the W. Indies, or vice
versa, and destroy a multitude of creatures? Of course I'm no judge, but
I thought De Candolle had made out his case about small areas of trees.
You will find at page 112, 3rd edition "Origin," a too concise allusion
to the Madeira flora being a remnant of the Tertiary European flora.
I shall feel deeply interested by reading your botanical difficulties
against occasional immigration. The facts you give about certain plants,
such as the heaths, are certainly very curious. (366/2. In Hooker's
lecture he gives St. Dabeoc's Heath and Calluna vulgaris as the most
striking of the few boreal plants in the Azores. Darwin seems to have
been impressed by the boreal character of the Azores, thus taking the
opposite view to that of Sir Joseph. See Letter 370, note.) I thought
the Azores flora was more boreal, but what can you mean by saying that
the Azores are nearer to Britain and Newfoundland than to Madeira?--on
the globe they are nearly twice as far off. (366/3. See Letter 368.)
With respect to sea currents, I formerly made enquiries at Madeira,
but cannot now give you the results; but I remember that the facts were
different from what is generally stated: I think that a ship wrecked on
the Canary Islands was thrown up on the coast of Madeira.

You speak as if only land-shells differed in Madeira and Porto Santo:
does my memory deceive me that there is a host of representative
insects?

When you exorcise at Nottingham occasional means of transport, be
honest, and admit how little is known on the subject. Remember how
recently you and others thought that salt water