'I am become a zealous disciple of Mr Lyell's views, as known in his admirable book. Geologising in South America, I am tempted to carry parts to a greater extent even than he does[102].' Before reaching home after his voyage, the duration of which was fortunately extended from two to five years, he had sent home letters asking to be elected a fellow of the Geological Society; and, immediately on his arrival, he gave up his zoological specimens to others and devoted his main energies for ten years to the working up of his geological notes and specimens. It may seem strange that the grandson of Erasmus Darwin should in early life have felt little or no interest in the question of the 'Origin of Species,' but such was certainly the case. He tells us in his autobiography that he had read his grandfather's _Zoonomia_ in his youth, without its producing any effect on him, and when at Edinburgh he says he heard his friend Robert Grant (afterwards Professor of Zoology in University College, London) as they were walking together 'burst forth in high admiration of Lamarck and his views on Evolution'--yet Darwin adds 'I listened in silent astonishment, and as far as I can judge without any effect on my mind[103].' The reason of this indifference towards his grandfather's works is obvious. All through his life, Darwin, like Lyell, showed a positive distaste for all speculation or theorising that was not based on a good foundation of facts or observations. In this respect, the attitude of Darwin's mind was the very opposite of that of Herbert Spencer--who, Huxley jokingly said, would regard as a 'tragedy'--'the killing of a beautiful theory by an ugly fact.' Darwin tells us himself that, while on his first reading of _Zoonomia_ he 'greatly admired' it--evidently on literary grounds--yet 'on reading it a second time after an interval of ten or fifteen years, I was much disappointed; _the proportion of speculation being so large to the facts given_.' Huxley who knew Charles Darwin so well in later years said of him that:-- 'He abhors mere speculation as nature abhors a vacuum. He is as greedy of cases and precedents as any constitutional lawyer, and all the principles he lays down are capable of being brought to the test of observation and experiment[104].' What then, we may ask, were the facts and observations which turned Darwin's mind towards the great problem that came to be the work of his after life? I think it is possible from the study of his letters and other published writings to give an answer to this very interesting question.