Letter from Darwin to Lyell...?

[Luis A. Ruedas]

Hoping this is the right forum...The other day I ran across a quote,
reportedly in a letter from Darwin to Lyell.  It was in an article on
Darwin by Loren Eiseley (Sci. Am., 1956).  Eiseley states: "...Nothing
would aid natural history more, he contended to Lyell, "than carefully
collecting and investigating of all the productions of the most
isolated islands.""

Would any of you out there have the text of the letter, or know where
such might be found?  I am rather interested in island faunas, and
would be curious to see the surrounding text.  Our library, I regret
to say, is not overly well furnished with Darwiniana.

Thanks

Luis A. Ruedas
Dept Biology
Cayey University College
University of Puerto Rico
Cayey, PR 00736