You may perhaps answer that Lombok is an outpost of an army that may
once have been as multitudinous as that of the old continent, but the
larger part of the host have been swamped in the Pacific. But they say
that European forms of animals and plants run wild in Australia and New
Zealand, whereas few of the latter can do the same in Europe. In my map
there is a small island called Nousabali; this ought to make the means
of migration of seeds and animals less difficult. I cannot find that you
say anywhere what is the depth of the sea between the Straits of Lombok,
but you mention that it exceeds 100 fathoms. I am quite willing to infer
that there is a connection between these soundings and the line of
demarcation between the two zoological provinces, but must we suppose
land communication for all birds of short flight? Must we unite South
America with the Galapagos Islands? Can you refer me to any papers by
yourself which might enlighten me and perhaps answer some of these
queries? I should have thought that the intercourse even of savage
tribes for tens of thousands of years between neighbouring islands would
have helped to convey in canoes many animals and plants from one
province to another so as to help to confound them. Your hypothesis of
the gradual advance of two widely separated continents towards each
other seems to be the best that can be offered. You say that a rise of
a hundred fathoms would unite the Philippine Islands and Bali to the
Indian region. Is there, then, a depth of 600 feet in that narrow strait
of Bali, which seems in my map only two miles or so in breadth?

I have [been] confined to the house for a week by a cold or I should
have tried to see you. I am afraid to go out to-day.--Believe me ever
most truly yours,

CHA. LYELL.