NATURE 



25 



THURSDAY, MAY 14, 1891. 



PRACTICAL GEOLOGY. 

 Aids in Practical Geology. By Grenville A. J. Cole, 

 F.G.S., Professor of Geology in the Royal College of 

 Science for Ireland. (London : C. Griffin and Co., 

 1891.) 

 An Introduction to the Study of Petrology: the Igneous 

 Rocks. By Frederick H. Hatch, Ph.D., F.G.S. (Lon- 

 don : Sonnenschein and Co., 1891.) 



HOWEVER prophetic may have been the far-seeing 

 premonitions of men in advance of their age in the 

 dim past, and however invaluable may have been the 

 additions made to the superstructure since, it can scarcely 

 be doubted that the foundation-stones of geology were 

 laid by Scotchmen and Englishmen towards the end of 

 the last, and during the earlier part of the present 

 century. And what a charm is there about the story of 

 these sturdy pioneers, not perhaps quite the men whom 

 one would have picked out as most fitted or most likely 

 to become the fathers of a new science. It has about it 

 the elements of a genuine romance. For the early train- 

 ing of few of these men was such as to give a scientific 

 bent to their mind ; they did not have what we are 

 pleased to call " the advantage of a scientific education " ; 

 it is probable that they never spoke, perhaps never 

 dreamed of, such a phrase as " the scientific method," 

 which we are so fond of formularizing, and on which we 

 plume ourselves somewhat. But in spite of these seeming 

 drawbacks, rather perhaps because with these men genius 

 was allowed to run its spontaneous untrammelled course, 

 they opened out to mankind a domain of knowledge the 

 very outskirts of which had been barely touched upon 

 before. Of shrewd mother-wit were they ; too keen of 

 eye to be wrong about their facts ; not a few were ardent 

 sportsmen, and the same instinct which led them to ride 

 straight to hounds or patiently and warily to stalk the 

 deer, led them also, as they brushed away minor details, 

 to go direct to main issues, and carried them on, without 

 rest but without haste, through the toils of many a year's 

 steady field-work. With what awe and reverence do we 

 look up to these giants when we pass their achievements 

 in review ! 



Nor does it one whit impair this feeling of respectful 

 admiration to turn to the other side, and cast a glance at 

 what were their unavoidable shortcomings. They were too 

 hard-headed to be illogical in the matter of straightforward 

 inferences, but it was hardly to be expected that they would 

 escape going astray sometimes when they ventured on 

 recondite speculation. Rough is not the word for their 

 method ; incomplete would be nearer the mark, but even 

 that can scarcely be applied when the means at their dis- 

 posal are taken into account. No one had yet taught the 

 value of the microscope and balance to the geologist ; 

 and, when these and other instruments of precision were 

 introduced, there was just a tendency to gird at appli- 

 ances that had a finnicking look abput them to Titans who 

 had so long and so successfully relied on their hammers 

 and their wits. 



But by degrees it became clear in Germany, and later 

 on in England, that, though the great main roads of the 

 NO. I 1 24, VOL. 44] 



newly- discovered territory had been tracked out with 

 such brilliant success, methods more refined than had 

 sufficed for pioneering work must be introduced if all 

 the intricacies of its lanes and by-ways were to be ex- 

 plored. Then the swing of the pendulum rather tended 

 to bring about a disposition to exalt the new means of 

 investigation, and there was just a risk that the sound 

 basis of field-work might come to be undervalued if not 

 neglected ; and that Mineralogy and Petrology, instead 

 of being the handmaids of Geology, might be thought to 

 constitute the whole of that science. But the mischief 

 never went far. The mantle which had fallen from the 

 shoulders of the great fathers was not to be lightly cast 

 aside ; and, while every new aid was cordially welcomed, 

 the conviction grew stronger and stronger that honest 

 work in the field must for ever be the starting-point of 

 geological inquiry. 



How thoroughly this truth has become engrained in 

 the minds of geologists is seen directly we open Prof. 

 Cole's " Aids in Practical Geology." A large part of the 

 book is taken up with minute and precise directions for 

 carrying out the various kinds of microscopical, optical, 

 and chemical examination of minerals and rocks. But 

 on the first page we read — 



" Such aids in determinative geology as are given in 

 the following pages may be applied in any halting-place, 

 or in cities after the return from an expedition ; but, in 

 any case, observations made on specimens are of slight 

 importance if uncoupled with knowledge of their true 

 position in the field." 



And again — 



" After a study of a number of type specimens, the 

 student is recommended to go out to some well- described 

 district, and to endeavour to recognize the varieties of 

 igneous and sedimentary ^ocks by careful observation in 

 the field. In this way alone can he appreciate the various 

 modes of weathering, the massive or minuter structures 

 due to jointing, the smooth or rugged outlines that cha- 

 racterize the masses of which his hand-specimens form a 

 part. . . . Nothing short of striking the rock-mass in 

 situ with the hammer, and taking in with the eye its 

 position and surroundings, even to the broader features 

 of the landscape, should content the geologist who would 

 follow worthily the founders and masters of the science." 



Again and again the author reiterates the lesson — 

 "Just as no mountain mass can be described by a 

 stranger from a number of hand-specimens, however 

 beautiful, so no rock can be adequately described from 

 isolated microscopic sections. Again and again the 

 observer will pass from his section to the solid specimen, 

 and from this, in memory at any rate, to the great mass 

 of which it formed a part." 



And in dealing with the nomenclature of igneous rocks, 

 the chaotic state of which is so largely due to the ignoring 

 of their field-relations, it is insisted that — 



" The following out of an igneous rock in the field is a 

 most important lesson, and will soon determine what is 

 valuable and what is valueless in any proposed scheme of 

 classification." 



That the author, in these and similar passages, is not 

 speaking from hearsay, not merely re-echoing what is now 

 a truism, is shown by the admirable practical directions 

 which he gives in the first chapter for the outfit and pro- 

 cedure of the field-geologist. Here, and indeed through- 

 out the book, the instructions are detailed and precise 



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