From the Darwin Correspondence Project:
"The main feature of the site is an online database with the complete, searchable, texts of around 5,000 letters written by and to Charles Darwin up to the year 1865. This includes all the surviving letters from the Beagle voyage - online for the first time - and all the letters from the years around the publication of Origin of species in 1859."You can search by subject, correspondent, or date, and there is a nice section devoted to Darwin and religion. For fun, I did a search on "asses" and came up with a letter to J.D. Hooker with the following quote in it:
"Thank you much for thinking about Asses & Mules: the forked stripe on shoulder is a very curious point (& I have seen traces of it) for the meaning of the fork is plain when the legs are transversely barred, but is an absurdity (except on doctrine of inheritance) with an animal with unstriped legs."Yes, I am very mature.