January 19, 1905J 



NA TURE 



207 



AN AMERICAN TEXT-BOOK OF GEOLOGY. 



Geology. Bv Thomas C. Chamberlin and RoUin D. 

 Salisbury. \ol. i. Geologic Processes and their 

 Results. Pp. .xix + 654; with 24 plates and 471 

 fifi^ures in the text. (New York : H. Holt and Co., 

 K104.) 



THE work of which this is the first volume, bear- 

 ing- the names of two well known professors in 

 the University of Chicago, is addressed to the mature 

 student, and is designed " to present an outline of the 

 salient features of geology, as now developed." The 

 present instalment, dealing with the nature and results 

 of the processes now in operation upon the globe, will 

 naturally prepare the way for the second volume, to 

 be devoted to tracing the history of past ages. Agree- 

 ing with other writers in approaching the science from 

 this side, the authors have been led by their own ex- 

 perience as teachers to depart somewhat from the 

 beaten track in their general plan of treatment, as well 

 .-IS in the relative importance assigned to certain specific 

 subjects. They tell us in their preface that they have 

 laid little stress on the generally recognised divisions 

 of geology, "dynamical," "structural," "strati- 

 graphical," &c., but have tried rather to emphasise the 

 historical element even in the discussion of special 

 themes, thus bringing out the essential unity of the 

 science. Again, some subjects, such as the develop- 

 ment of drainage-systems, the ultimate cause of 

 crust-movements, and others, receive here fuller 

 treatment than has been customary in works of this 

 scope. 



Most of the original features of the book we heartily 

 welcome. We think, too, that the authors have 

 generally been happy in their treatment of the more 

 dubious and debatable problems of physical geology. 

 Their design in this has been freely to introduce the 

 theoretical element when necessary, and at the same 

 time " to avoid confusing the interpretations based on 

 hypothesis with the statements of fact and established 

 doctrines." \\'here important differences of opinion 

 exist, the alternative hypotheses are set forth and their 

 consequences compared. In some instances this 

 candour is pushed rather far, as when the cause of 

 vulcanism is discussed on seven distinct hypotheses. 

 Having regard to the class of students for whom the 

 book is primarily intended, we think that the authors 

 have needlessly hampered themselves by trying to 

 make it intelligible to one who has had no previous 

 acquaintance with the rudiments of geology. How far 

 they have succeeded in this it is not easy to judge. 

 Thus the technical terms of the field-geologist, " dip," 

 " anticline," " dyke " and the like, are not formally 

 defined until we reach a late section of the volume, but 

 the conceptions implied have necessarily been intro- 

 duced much earlier. Such difficulties inevitably 

 confront the writer of an elementary class-book, but 

 they might safely be ignored in a work like the 

 present. 



After a preliminary outline of the general scope of 

 geology, the authors proceed to discuss in turn the 

 geological effects of the atmosphere, of running water, 

 NO. 1838, VOL 71] 



of underground water, of snow and ice, and of the 

 ocean. Their clear exposition of the mechanism of 

 rain- and river-erosion, with due regard to the con- 

 trolling conditions, is an admirable summarv of a 

 fundamental part of geology which in nio>t of our 

 text-books receives very inadequate treatment. It is 

 written on modern lines, the fertile conception of the 

 "base-level of erosion," with its important conse- 

 quences, being introduced at an early stage. The sub- 

 ject is one which American geologists, with their un- 

 rivalled opportunities, have made peculiarly their own, 

 and it could scarcely have fallen into better hands. 

 The other geological agents are discussed in the same 

 comprehensive but concise manner, and the chapter 

 dealing with glacial action is, as might be expected 

 from the authors, of special interest. 



The chapter on movements and deformations of the 

 earth's body contains much material which is not else- 

 where accessible to the student in a connected shape, 

 and some originality appears in matter as well as in 

 treatment. Consideration of the possible causes of 

 the great crust-movements leads to an inquiry into the 

 original and present distributions of temperature in 

 the globe, and to a comparison of the nebular hvpo- 

 thesis with that of "accretion." The comparison is 

 presented in a judicial manner, and the enunciation of 

 the accretion hypothesis is tantalisingly brief; but a 

 fuller discussion is promised in the second volume. 

 Geologists sometimes need to be reminded that cosmo- 

 gony is a legitimate part of their province, not to be 

 surrendered without good reason shown. .At least it 

 is well that students should see just how much of 

 accepted physical principles and how much of arbitrarv 

 assumptions go to the building of dogmas which have 

 carried alarm into some quarters. 



The treatment accorded to igneous action seems to us 

 in some respects unsatisfactory. Descriptive petro- 

 graphy is, no doubt wisely, represented by a brief 

 summary, an appendix to a generalised account of 

 " the origin and descent of rocks." But what follows 

 seems to lack due proportion. " Vulcanism " is used 

 to include intrusive as well as extrusive action, but 

 the chapter is occupied almost exclusively with the 

 latter. The plutonic and other igneous intrusions, the- 

 varied forms which they assume, and their intimate 

 relation to crust-movements and to geological history 

 in general, are dismissed almost without notice. The 

 full and admirable discussion of volcanoes might thus 

 give a student the impression that these superficial 

 phenomena are the only important effects of igneous 

 activity. 



The volume concludes with a chapter on the geologic 

 functions of life, and a good index is added. The book 

 is issued in handsome form ; but the highlv glazed 

 paper, presumably adopted for the sake of the figures, 

 is irritating to the reader. The abundant figures, 

 selected from various sources, are well chosen to illus- 

 trate the text, and well reproduced. The subjects are 

 for the most part -American. A useful feature is the 

 illustration of various types of topography by actual 

 maps, taken from the beautifully contoured sheets of 

 the United States Geological .Survey. A. H. 



