The Critical Introduction begins: "Of the remarkable "trilogy" constituted by Darwin's writings which deal with the geology of the "Beagle," the member which has perhaps attracted least attention, up to the present time is that which treats of the geology of South America. The actual writing of this book appears to have occupied Darwin a shorter period than either of the other volumes of the series; his diary records that the work was accomplished within ten months, namely, between July 1844 and April 1845; but the book was not actually issued till late in the year following, the preface bearing the date "September 1846." Altogether, as Darwin informs us in his "Autobiography," the geological books "consumed four and a half years' steady work," most of the remainder of the ten years that elapsed between the return of the "Beagle," and the completion of his geological books being, it is sad to relate, "lost through illness!"
