"The number of intermediate varieties which have formerly existed on earth must be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory." - Charles Darwin 1902 edition.
“…I am quite conscious that my speculations run beyond the bounds of true science….It is a mere rag of an hypothesis with as many flaw & holes as sound parts.” Charles Darwin to Asa Gray, cited by Adrian Desmond and James Moore, Darwin, (New York: W.W. Norton and Company, 1991) pp. 456, 475.