Some Creationist books have this quote:
"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 serious objection which can be urged against the theory."Darwin's book did not end there. The next two sentences were:
The Origin of Species (1859) in Chapter 10, On the imperfection of the geologic record.
The explanation lies, as I believe, in the extreme imperfection of the geological record.He went on to give a nice example of how an actual ancestor might not be what one expected. Darwin did, after all, believe his own theory. He saw problems, but not insuperable ones.
In the first place, it should always be borne in mind what sort of intermediate forms must, on the theory, have formerly existed
With modern hindsight, his strongest counter was that fossil series were rare, and that some would be found in the future. By now, 130 years later, we have found quite a number.