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undoubtedly an admirable preparation for his future work as an explorer； but in none of his letters of this period does he even mention geology。 He says； however； 〃I was so sickened with lectures at Edinburgh that I did not even attend Sedgwick's eloquent and interesting lectures。〃 （〃L。L。〃 I。 page 48。）
It was only after passing his examination； and when he went up to spend two extra terms at Cambridge； that geology again began to attract his attention。 The reading of Sir John Herschel's 〃Introduction to the Study of Natural Philosophy〃； and of Humboldt's 〃Personal Narrative〃； a copy of which last had been given to him by his good friend and mentor Henslow； roused his dormant enthusiasm for science； and awakened in his mind a passionate desire for travel。 And it was from Henslow； whom he had accompanied in his excursions； but without imbibing any marked taste； at that time； for botany； that the advice came to think of and to 〃begin the study of geology。〃 （〃L。L。〃 I。 page 56。） This was in 1831； and in the summer vacation of that year we find him back again at Shrewsbury 〃working like a tiger〃 at geology and endeavouring to make a map and section of Shropshirework which he says was not 〃as easy as I expected。〃 （〃L。L。〃 I。 page 189。） No better field for geological studies could possibly be found than Darwin's native county。
Writing to Henslow at this time； and referring to a form of the instrument devised by his friend； Darwin says： 〃I am very glad to say I think the clinometer will answer admirably。 I put all the tables in my bedroom at every conceivable angle and direction。 I will venture to say that I have measured them as accurately as any geologist going could do。〃 But he adds： 〃I have been working at so many things that I have not got on much with geology。 I suspect the first expedition I take； clinometer and hammer in hand； will send me back very little wiser and a good deal more puzzled than when I started。〃 （〃L。L。〃 I。 page 189。） Valuable aid was； however； at hand； for at this time Sedgwick； to whom Darwin had been introduced by the ever…helpful Henslow； was making one of his expeditions into Wales； and consented to accept the young student as his companion during the geological tour。 （〃L。L。〃 I。 page 56。） We find Darwin looking forward to this privilege with the keenest interest。 （〃L。L。〃 I。 page 189。）
When at the beginning of August （1831）； Sedgwick arrived at his father's house in Shrewsbury； where he spent a night； Darwin began to receive his first and only instruction as a field…geologist。 The journey they took together led them through Llangollen； Conway； Bangor； and Capel Curig； at which latter place they parted after spending many hours in examining the rocks at Cwm Idwal with extreme care； seeking for fossils but without success。 Sedgwick's mode of instruction was admirablehe from time to time sent the pupil off on a line parallel to his own； 〃telling me to bring back specimens of the rocks and to mark the stratification on a map。〃 （〃L。L。〃 I。 page 57。） On his return to Shrewsbury； Darwin wrote to Henslow； 〃My trip with Sedgwick answered most perfectly；〃 （〃L。L。〃 I。 page 195。）； and in the following year he wrote again from South America to the same friend； 〃Tell Professor Sedgwick he does not know how much I am indebted to him for the Welsh expedition； it has given me an interest in Geology which I would not give up for any consideration。 I do not think I ever spent a more delightful three weeks than pounding the north…west mountains。〃 （〃L。L。〃 I。 pages 237…8。）
It would be a mistake； however； to suppose that at this time Darwin had acquired anything like the affection for geological study； which he afterwards developed。 After parting with Sedgwick； he walked in a straight line by compass and map across the mountains to Barmouth to visit a reading party there； but taking care to return to Shropshire before September 1st； in order to be ready for the shooting。 For as he candidly tells us； 〃I should have thought myself mad to give up the first days of partridge… shooting for geology or any other science！〃 （〃L。L。〃 I。 page 58。）
Any regret we may be disposed to feel that Darwin did not use his opportunities at Edinburgh and Cambridge to obtain systematic and practical instruction in mineralogy and geology； will be mitigated； however； when we reflect on the danger which he would run of being indoctrinated with the crude 〃catastrophic〃 views of geology； which were at that time prevalent in all the centres of learning。
Writing to Henslow in the summer of 1831； Darwin says 〃As yet I have only indulged in hypotheses； but they are such powerful ones that I suppose； if they were put into action but for one day； the world would come to an end。〃 （〃L。L。〃 I。 page 189。）
May we not read in this passage an indication that the self…taught geologist had； even at this early stage； begun to feel a distrust for the prevalent catastrophism； and that his mind was becoming a field in which the seeds which Lyell was afterwards to sow would 〃fall on good ground〃？
The second period of Darwin's geological careerthe five years spent by him on board the 〃Beagle〃was the one in which by far the most important stage in his mental development was accomplished。 He left England a healthy； vigorous and enthusiastic collector； he returned five years later with unique experiences； the germs of great ideas； and a knowledge which placed him at once in the foremost ranks of the geologists of that day。 Huxley has well said that 〃Darwin found on board the 〃Beagle〃 that which neither the pedagogues of Shrewsbury； nor the professoriate of Edinburgh； nor the tutors of Cambridge had managed to give him。〃 （〃Proc。 Roy。 Soc。〃 Vol。 XLIV。 （1888）； page IX。） Darwin himself wrote； referring to the date at which the voyage was expected to begin： 〃My second life will then commence； and it shall be as a birthday for the rest of my life。〃 （〃L。L。〃 I。 page 214。）； and looking back on the voyage after forty years； he wrote； 〃The voyage of the 'Beagle' has been by far the most important event in my life； and has determined my whole career；。。。I have always felt that I owe to the voyage the first real training or education of my mind； I was led to attend closely to several branches of natural history； and thus my powers of observation were improved； though they were always fairly developed。〃 （〃L。L。〃 I。 page 61。）
Referring to these general studies in natural history； however； Darwin adds a very significant remark： 〃The investigation of the geology of the places visited was far more important； as reasoning here comes into play。 On first examining a new district nothing can appear more hopeless than the chaos of rocks； but by recording the stratification and nature of the rocks and fossils at many points； always reasoning and predicting what will be found elsewhere； light soon begins to dawn on the district； and the structure of the whole becomes more or less intelligible。〃 （〃L。L。〃 I。 page 62。）
The famous voyage began amid doubts； discouragements and disappointments。 Fearful of heart…disease； sad at parting from home and friends； depressed by sea…sickness； the young explorer； after being twice driven back by baffling winds； reac