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him at Down。 In the postscript of a letter （of April 15； 1880） arranging one of these visits； he writes： 〃Since poor； dear Lyell's death； I rarely have the pleasure of geological talk with anyone。〃）
In one of the very interesting conversations which I had with Charles Darwin during the last seven years of his life； he asked me in a very pointed manner if I were able to recall the circumstances； accidental or otherwise； which had led me to devote myself to geological studies。 He informed me that he was making similar inquiries of other friends； and I gathered from what he said that he contemplated at that time a study of the causes producing SCIENTIFIC BIAS in individual minds。 I have no means of knowing how far this project ever assumed anything like concrete form； but certain it is that Darwin himself often indulged in the processes of mental introspection and analysis； and he has thus fortunately left usin his fragments of autobiography and in his correspondencethe materials from which may be reconstructed a fairly complete history of his own mental development。
There are two perfectly distinct inquiries which we have to undertake in connection with the development of Darwin's ideas on the subject of evolution：
FIRST。 How； when； and under what conditions was Darwin led to a conviction that species were not immutable； but were derived from pre…existing forms？
SECONDLY。 By what lines of reasoning and research was he brought to regard 〃natural selection〃 as a vera causa in the process of evolution？
It is the first of these inquiries which specially interests the geologist； though geology undoubtedly played a partand by no means an insignificant partin respect to the second inquiry。
When； indeed； the history comes to be written of that great revolution of thought in the nineteenth century； by which the doctrine of evolution； from being the dream of poets and visionaries； gradually grew to be the accepted creed of naturalists； the paramount influence exerted by the infant science of geologyand especially that resulting from the publication of Lyell's epoch…making work； the 〃Principles of Geology〃cannot fail to be regarded as one of the leading factors。 Herbert Spencer in his 〃Autobiography〃 bears testimony to the effect produced on his mind by the recently published 〃Principles〃； when； at the age of twenty； he had already begun to speculate on the subject of evolution （Herbert Spencer's 〃Autobiography〃； London； 1904； Vol。 I。 pages 175…177。）； and Alfred Russel Wallace is scarcely less emphatic concerning the part played by Lyell's teaching in his scientific education。 （See 〃My Life； a record of Events and Opinions〃； London； 1905； Vol。 I。 page 355； etc。 Also his review of Lyell's 〃Principles〃 in 〃Quarterly Review〃 （Vol。 126）； 1869； pages 359…394。 See also 〃The Darwin…Wallace Celebration by the Linnean Society〃 （1909）； page 118。） Huxley wrote in 1887 〃I owe more than I can tell to the careful study of the 〃Principles of Geology〃 in my young days。〃 （〃Science and Pseudo Science〃； 〃Collected Essays〃； London； 1902； Vol。 V。 page 101。） As for Charles Darwin； he never tiredeither in his published writings； his private correspondence or his most intimate conversationsof ascribing the awakening of his enthusiasm and the direction of his energies towards the elucidation of the problem of development to the 〃Principles of Geology〃 and the personal influence of its author。 Huxley has well expressed what the author of the 〃Origin of Species〃 so constantly insisted upon； in the statements 〃Darwin's greatest work is the outcome of the unflinching application to Biology of the leading idea and the method applied in the 〃Principles〃 to Geology （〃Proc。 Roy。 Soc。〃 Vol。 XLIV。 （1888）； page viii。； 〃Collected Essays〃 II。 page 268； 1902。）； and 〃Lyell； for others； as for myself； was the chief agent in smoothing the road for Darwin。〃 （〃Life and Letters of Charles Darwin〃 II。 page 190。）
We propose therefore to consider； first； what Darwin owed to geology and its cultivators； and in the second place how he was able in the end so fully to pay a great debt which he never failed to acknowledge。 Thanks to the invaluable materials contained in the 〃Life and Letters of Charles Darwin〃 （3 vols。） published by Mr Francis Darwin in 1887； and to 〃More Letters of Charles Darwin〃 （2 vols。） issued by the same author； in conjunction with Professor A。C。 Seward； in 1903； we are permitted to follow the various movements in Darwin's mind； and are able to record the story almost entirely in his own words。 （The first of these works is indicated in the following pages by the letters 〃L。L。〃； the second by 〃M。L。〃）
From the point of view of the geologist； Darwin's life naturally divides itself into four periods。 In the first； covering twenty…two years； various influences were at work militating； now for and now against； his adoption of a geological career； in the second periodthe five memorable years of the voyage of the 〃Beagle〃the ardent sportsman with some natural…history tastes； gradually became the most enthusiastic and enlightened of geologists； in the third period； lasting ten years； the valuable geological recruit devoted nearly all his energies and time to geological study and discussion and to preparing for publication the numerous observations made by him during the voyage； the fourth period； which covers the latter half of his life； found Darwin gradually drawn more and more from geological to biological studies； though always retaining the deepest interest in the progress and fortunes of his 〃old love。〃 But geologists gladly recognise the fact that Darwin immeasurably better served their science by this biological work； than he could possibly have done by confining himself to purely geological questions。
From his earliest childhood； Darwin was a collector； though up to the time when； at eight years of age； he went to a preparatory school； seals； franks and similar trifles appear to have been the only objects of his quest。 But a stone； which one of his schoolfellows at that time gave to him； seems to have attracted his attention and set him seeking for pebbles and minerals； as the result of this newly acquired taste； he says （writing in 1838） 〃I distinctly recollect the desire I had of being able to know something about every pebble in front of the hall doorit was my earliest and only geological aspiration at that time。〃 （〃M。L。〃 I。 page 3。） He further suspects that while at Mr Case's school 〃I do not remember any mental pursuits except those of collecting stones；〃 etc。。。〃I was born a naturalist。〃 （〃M。L。〃 I。 page 4。）
The court…yard in front of the hall door at the Mount House； Darwin's birthplace and the home of his childhood； is surrounded by beds or rockeries on which lie a number of pebbles。 Some of these pebbles （in quite recent times as I am informed） have been collected to form a 〃cobbled〃 space in front of the gate in the outer wall； which fronts the hall door； and a similar 〃cobbled area；〃 there is reason to believe； may have existed in Darwin's childhood before the door itself。 The pebbles； which were obtained from a neighbouring gravel…pit； being derived from the glacial drift； exhibit very striking differences in colour and form。 It was probably this circumstance which awakened in the child his love of observation and speculation。 It is certainly remarkable that 〃aspirations〃 of the kind should have arisen in the mind of a child of 9 or 10！
When he went to Shrewsbury School； he relates 〃I continued collecting minerals with much zeal； but quite unscientifically；all that I cared about was a new…NAMED mineral； and I hardly attempted to classify them。〃 （〃L。L。〃 I。 page 34。）
There has stood from very early times in Darwin's native town of Shrewsbury； a very notable boulder which has probably marked a boundary and is known as the 〃Bell…stone〃giving its name to a house and street。 Darwin tells us in his 〃Autobiography〃 that while he was at Shrewsbury School at the age of 13 or 14 〃an old Mr Cotton in Shropshire； who knew a good deal about rocks〃 pointed out to me 〃。。。the 'bell…stone'； he told me that there was no rock of the same kind nearer than Cumberland or Scotland； and he solemnly assured me that the world would come to an end before anyone would be able to explain how this stone came where it now lay〃！ Darwin adds 〃This produced a deep impression on me； and I meditated over this wonderful stone。〃 （〃L。L。〃 I。 page 41。）
The 〃bell…stone〃 has now； owing to the necessities of building； been removed a short distance from its original site； and is carefully preserved within the walls of a bank。 It is a block of irregular shape 3 feet long and 2 feet wide； and about 1 foot thick； weighing probably not less than one…third of a ton。 By the courtesy of the directors of the National Provincial Bank of England； I have been able to make a minute examination of it； and Professors Bonney and Watts； with Mr Harker and Mr Fearnsides have given me their valuable assistance。 The rock is a much altered andesite and was probably derived from the Arenig district in North Wales； or possibly from a point nearer the Welsh Border。 （I am greatly indebted to the Managers of the Bank at Shrewsbury for kind assistance in the examinatio