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When therefore the series of interesting monographs on plant-life had been completed, Darwin set to work in bringing the information that he had gradually accumulated during forty-four years to bear on the subject of his early paper. He also utilised the skill and ingenuity he had acquired in botanical work to aid in the elucidation of many of the difficulties that presented themselves. I well remember a visit which I paid to Down at this period. At the side of the little study stood flower-pots containing earth with worms, and, without interrupting our conversation, Darwin would from time to time lift the glass plate covering a pot to watch what was going on. Occasionally, with a humorous smile, he would murmur something about a book in another room, and slip away; returning shortly, without the book but with unmistakeable signs of having visited the snuff-jar outside. After working about a year at the worms, he was able at the end of 1881 to publish the charming little book--"The Formation of Vegetable Mould through the Action of Worms, with Observations on their Habits". This was the last of his books, and its reception by reviewers and the public alike afforded the patient old worker no little gratification. Darwin's scientific career, which had begun with geological research, most appropriately ended with a return to it.

It has been impossible to sketch the origin and influence of Darwin's geological work without, at almost every step, referring to the part played by Lyell and the "Principles of Geology". Haeckel, in the chapters on Lyell and Darwin in his "History of Creation", and Huxley in his striking essay "On the Reception of the Origin of Species" ("L.L." II. pages 179- 204.) have both strongly insisted on the fact that the "Origin" of Darwin was a necessary corollary to the "Principles" of Lyell.

It is true that, in an earlier essay, Huxley had spoken of the doctrine of Uniformitarianism as being, in a certain sense, opposed to that of Evolution (Huxley's Address to the Geological Society, 1869. "Collected Essays", Vol. VIII. page 305, London, 1896.); but in his later years he took up a very different and more logical position, and maintained that "Consistent uniformitarianism postulates evolution as much in the organic as in the inorganic world. The origin of a new species by other than ordinary agencies would be a vastly greater 'catastrophe' than any of those which Lyell success fully eliminated from sober geological speculation." ("L.L." II. page 190.)

Huxley's admiration for the "Principles of Geology", and his conviction of the greatness of the revolution of thought brought about by Lyell, was almost as marked as in the case of Darwin himself. (See his Essay on "Science and Pseudo Science". "Collected Essays", Vol. V. page 90, London, 1902.) He felt, however, as many others have done, that in one respect the very success of Lyell's masterpiece has been the reason why its originality and influence have not been so fully recognised as they deserved to be. Written as the book was before its author had arrived at the age of thirty, no less than eleven editions of the "Principles" were called for in his lifetime. With the most scrupulous care, Lyell, devoting all his time and energies to the task of collecting and sifting all evidence bearing on the subjects of his work, revised and re-revised it; and as in each edition, eliminations, modifications, corrections, and additions were made, the book, while it increased in value as a storehouse of facts, lost much of its freshness, vigour and charm as a piece of connected reasoning.

Darwin undoubtedly realised this when he wrote concerning the "Principles", "the first edition, my old true love, which I never deserted for the later editions." ("M.L." II. page 222.) Huxley once told me that when, in later life, he read the first edition, he was both surprised and delighted, feeling as if it were a new book to him. (I have before me a letter which illustrates this feeling on Huxley's part. He had lamented to me that he did not possess a copy of the first edition of the "Principles", when, shortly afterwards, I picked up a dilapidated copy on a bookstall; this I had bound and sent to my old teacher and colleague. His reply is characteristic:

You could not have made me a more agreeable present than the copy of the first edition of Lyell, which I find on my table. I have never been able to meet with the book, and your copy is, as the old woman said of her Bible, "the best of books in the best of bindings."

I cannot refrain from relating an incident which very strikingly exemplifies the affection for one another felt by Lyell and Huxley. In his last illness, when confined to his bed, Lyell heard that Huxley was to lecture at the Royal Institution on the "Results of the 'Challenger' expedition": he begged me to attend the lecture and bring him an account of it. Happening to mention this to Huxley, he at once undertook to go to Lyell in my place, and he did so on the morning following his lecture. I shall never forget the look of gratitude on the face of the invalid when he told me, shortly afterwards, how Huxley had sat by his bedside and "repeated the whole lecture to him.")

Darwin's generous nature seems often to have made him experience a fear lest he should do less than justice to his "dear old master," and to the influence that the "Principles of Geology" had in moulding his mind. In 1845 he wrote to Lyell, "I have long wished, not so much for your sake, as for my own feelings of honesty, to acknowledge more plainly than by mere reference, how much I geologically owe you. Those authors, however, who like you, educate people's minds as well as teach them special facts, can never, I should think, have full justice done them except by posterity, for the mind thus insensibly improved can hardly perceive its own upward ascent." ("L.L." I. pages 337-8.) In another letter, to Leonard Horner, he says: "I always feel as if my books came half out of Lyell's brain, and that I never acknowledge this sufficiently." ("M.L." II. page 117.) Darwin's own most favourite book, the "Narrative of the Voyage", was dedicated to Lyell in glowing terms; and in the "Origin of Species" he wrote of "Lyell's grand work on the "Principles of Geology", which the future historian will recognise as having produced a revolution in Natural Science." "What glorious good that work has done" he fervently exclaims on another occasion. ("L.L." I. page 342.)