he had been putting together, and introduced questions that had to be dealt with. He responded that he had been "somewhat less amused at it .... the writing & arrangement are certainly admirable, but his geology strikes me as bad, & his zoology far worse. Darwin had learnt geology from Adam Sedgwick, and was particularly interested in what his former mentor had to say about evolution. In October 1845 he wrote to his friend Charles Lyell that Sedgwick's review was a "grand piece of argument against mutability of species" which he had read with "fear & trembling," but had been "well pleased to find" that he had anticipated Sedgwick's objections and "had not overlooked any of the arguments". He read Explanations early in 1846 and thought "the spirit of [it], though not the facts, ought to shame Sedgwick", while noting speculation and evidence suggesting that Chambers had written the books. In April 1847, after meeting Chambers then subsequently receiving a presentation of Vestiges, Darwin became convinced that Chambers must have been the author. In his introduction to On the Origin of Species, published in 1859, Darwin assumed that his readers were aware of Vestiges, and wrote identifying what he felt was one of its gravest deficiencies with regards to its theory of biological evolution: The author of the 'Vestiges of Creation' would, I presume, say that, after a certain unknown number of generations, some bird had given birth to a woodpecker, and some plant to the mistletoe, and that these had been produced perfect as we now see them; but this assumption seems to me to be no explanation, for it leaves the case of the coadaptations of organic beings to each other and to their physical conditions of life, untouched and unexplained. Chambers took the publication of the Origin as an opportunity to release a new edition of Vestiges and respond to Darwin's comments, lamenting that Darwin had misunderstood the Vestiges. "It seems to the author," Chambers wrote, "that Mr. Darwin has only been enabled by his infinitely superior knowledge to point out a principle in what may be called practical animal life, which appears capable of bringing about the modifications theoretically assumed in the earlier work. His book, in no essential respect, contradicts the present: on the contrary...it expresses substantially the same general ideas." In perhaps a gross simplification, Chambers concludes that "The difference seems to be in