element colonising that side of the continent so much as the eastern side;
or will climate suffice? I shall to the day of my death keep up my full
interest in Geographical Distribution, but I doubt whether I shall ever
have strength to come in any fuller detail than in the "Origin" to this
grand subject. In fact, I do not suppose any man could master so
comprehensive a subject as it now has become, if all kingdoms of nature are
included. I have read Murray's book, and am disappointed--though, as you
said, here and there clever thoughts occur. How strange it is, that his
view not affording the least explanation of the innumerable adaptations
everywhere to be seen apparently does not in the least trouble his mind.
One of the most curious cases which he adduces seems to me to be the two
allied fresh-water, highly peculiar porpoises in the Ganges and Indus; and
the more distantly allied form of the Amazons. Do you remember his
explanation of an arm of the sea becoming cut off, like the Caspian,
converted into fresh-water, and then divided into two lakes (by upheaval),
giving rise to two great rivers. But no light is thus thrown on the
affinity of the Amazon form. I now find from Flower's paper (384/3.
"Zoolog. Trans." VI., 1869, page 115. The toothed whales are divided into
the Physeteridae, the Delphinidae, and the Platanistidae, which latter is
placed between the two other families, and is divided into the sub-families
Iniinae and Platanistinae.) that these fresh-water porpoises form two sub-
families, making an extremely isolated and intermediate, very small family.
Hence to us they are clearly remnants of a large group; and I cannot doubt
we here have a good instance precisely like that of ganoid fishes, of a
large ancient marine group, preserved exclusively in fresh-water, where
there has been less competition, and consequently little modification.
(384/4. See Volume I., Letter 95.) What a grand fact that is which Miquel
gives of the beech not extending beyond the Caucasus, and then reappearing
in Japan, like your Himalayan Pinus, and the cedar of Lebanon. (384/5. For
Pinus read Deodar. The essential identity of the deodar and the cedar of