Gray, Asa. 1861. Natural Selection not inconsistent with Natural Theology. A free examination of Darwin's treatise on the Origin of Species, and of its American reviewers. Reprinted from the Atlantic monthly for July, August, and October, 1860. London: Trübner & Co., Boston: Ticknor and Fields. http://darwin-online.org.uk/content/frameset?pageseq=1&itemID=A567&viewtype=text
Darwin (1871), pp 385–405; Browne (2002), pp 339–343
Darwin (1887), pp 145–133; Browne (2002), pp 359–369