which some of the so-called extinct species have never passed
into recent ones."

Again, the following remarkable passage occurs in the postscript
of a letter addressed to Sir John Herschel in 1836:--

"In regard to the origination of new species, I am very glad to
find that you think it probable that it may be carried on through
the intervention of intermediate causes. I left this rather to
be inferred, not thinking it worth while to offend a certain
class of persons by embodying in words what would only be a
speculation." (In the same sense, see the letter to Whewell,
March 7, 1837, volume ii., page 5:--

"In regard to this last subject [the changes from one set of
animal and vegetable species to another]...you remember what
Herschel said in his letter to me. If I had stated as plainly as
he has done the possibility of the introduction or origination of
fresh species being a natural, in contradistinction to a
miraculous process, I should have raised a host of prejudices
against me, which are unfortunately opposed at every step to any
philosopher who attempts to address the public on these
mysterious subjects." See also letter to Sedgwick, January 12,
1838 ii. page 35.) He goes on to refer to the criticisms which
have been directed against him on the ground that, by leaving
species to be originated by miracle, he is inconsistent with his
own doctrine of uniformitarianism; and he leaves it to be
understood that he had not replied, on the ground of his general
objection to controversy.