When talking with Lyell at this time about the opposition of the old school of geologists to their joint views, Darwin said, 'What a good thing it would be if every scientific man was to die at sixty years old, as afterwards he would be sure to oppose all new doctrines[72].' In conversations that I had with him late in life, Darwin several times remarked to me, that 'he had seen so many of his friends make fools of themselves by putting forward new theoretical views in their old age, that he had resolved quite early in life, never to publish any speculative opinions after he was sixty.' But both in conversation and in his writings he always maintained that Lyell was an exception to all such rules, seeing that at last he adopted the theory of Natural Selection in his old age, thus displaying the most 'remarkable candour.' All who had the pleasure of discussing geological questions with Lyell will recognise the truth of the portrait drawn of his old friend by Darwin, about a year before his own death. He says:-- 'His mind was characterised, as it appeared to me, by clearness, caution, sound judgment, and a good deal of originality. When I made a remark to him on Geology, he never rested until he saw the whole case clearly, and often made me see it more clearly than I had done before.' And he sums up his admiration of the 'dear old master' in the words 'The science of Geology is enormously indebted to Lyell--more so, as I believe, than to any other man who ever lived[73].' Alfred Russel Wallace is scarcely less emphatic than Charles Darwin himself in his expression of affection and admiration for Lyell, and his indebtedness to the _Principles of Geology_. In his Autobiography, Wallace writes:-- 'With Sir Charles I soon felt at home, owing to his refined and gentle manners, his fund of quiet humour, and his intense love and extensive knowledge of natural science. His great liberality of thought and wide general interests were also attractive to me; and although when he had once arrived at a definite conclusion, he held by it very tenaciously until a considerable body of well-ascertained facts could be adduced against it, yet he was always willing to listen to the arguments of his opponents, and to give them careful and repeated consideration[74].' Of the influence of the _Principles of Geology_ in leading him to evolution, he wrote: