NA TURE 



409 



THURSDAY, AUGUST 30, il 



THEORETICAL GEOLOGY. 



Theoretische Geologie. Von Dr. E. Reyer, A. O. Prof, 

 der Geologie an der Universitat Wien. (Stuttgart, 

 E. Schweitzerbart'sche Verlagshandlung, 1888.) 



IT would be most unfair to compare the work before us 

 with any of the numerous treatises on geological 

 science which have during recent years made their 

 appearance in England, Germany, and France. The 

 author's aim, as defined in his preface, has been not so 

 much to give a well-proportioned summary of the ascer- 

 tained facts of the science, as to prepare an historical and 

 critical review of the ideas that have been put forward 

 concerning the fundamental principles of geology. To 

 find a parallel to the present essay, indeed, we should 

 have to go back to the " Philosophic der Geologie " 

 of Vogelsang, or even to the works of Lyell and Von 

 Hoff. 



Those who are familiar with Dr. Reyer's earlier works 

 — " Die Euganeen : Bau und Geschichte eines Vulcanes," 

 and " Beitrag zur Fysik der Eruptionen und der Eruptiv- 

 Gesteine " — will be prepared to find the problems of 

 geology treated by the author, not only with great fullness 

 of knowledge, but with a remarkable freedom from the 

 influence of traditional modes of thought ; and they will 

 not be disappointed by the perusal of the present volume. 

 Since the period when his earlier works appeared, Dr. 

 Reyer has travelled very extensively, and has had the 

 fortunate opportunity of studying those splendid mani- 

 festations of terrestrial forces which are found in the 

 Western Territories of the United States. Everywhere 

 the reader of this volume is enabled to profit by these 

 widened experiences of its author. 



In his preface, Dr. Reyer expresses a regret that there 

 does not exist in Germany the same class of private 

 students of science as is found in this country ; for to the 

 labours of men who have been alike free from the con- 

 servative pedantry of the professor and from the shallow 

 pretensions of the mere dilettante, he justly ascribes a 

 very great part of the credit of advancing geological 

 science in England. The author instances the names of 

 Hopkins and Herschel, but no one acquainted with the 

 history of geology will fail to add those of Hutton, Sir 

 James Hall, William Smith, Scrope, De la Beche, 

 Conybeare, Lyell, Darwin, Godwin-Austen, Sorby, and a 

 host of others. Regret has sometimes, and not un- 

 justifiably, been expressed that the moulding of geological 

 thought has, during recent years, fallen more completely 

 into the hands of those who may be called professional 

 geologists— a result which is perhaps a necessary con- 

 sequence of the more specialized nature of the study at 

 the present day ; but we trust that the day is very far 

 distant when the advance of geological knowledge in 

 England will be wholly, or indeed mainly, dependent 

 on the labours of those engaged in teaching or in making 

 geological maps. 



Dr. Reyer seems to hold that it is almost impossible 

 that physical geology and palaeontology should be cul- 

 tivated and taught by the same individual, and he 

 Vol. xxxviii.— No. 983. 



advocates the practical divorce of these two branches 

 of science. It would not be difficult to point out objec- 

 tions to this course and serious difficulties in the way 

 of its adoption ; such difficulties must arise in the case 

 of rocks which are wholly or in part made up of the 

 remains of organisms, and in connection with questions 

 concerning the physical conditions under which certain 

 rock-masses have been accumulated, when these can only 

 be adequately discussed after the nature of the organic 

 remains inclosed in them has been taken into account. 

 Nevertheless, no one will contest the author's right to 

 limit the scope of his own discussions to purely physical 

 problems ; and, indeed, Dr. Reyer has found himself 

 compelled to confine the present volume to the questions 

 more or less directly connected with igneous activity 

 upon the globe, leaving the problems more especially 

 connected with the waters of the globe and those of 

 cosmical geology for future sections of the work. 



Commencing with an account of the explosive action of 

 volcanoes and of the circumstances connected with the 

 outflow of lava from them, the author, enlarging the scope 

 of the inquiry pursued in his former works, proceeds to 

 discuss the physical problems involved in these remarkable 

 phenomena. Observations made in recent years upon the 

 absorption of gases by molten metals and other sub- 

 stances, and the phenomena attending the escape of the 

 gases from such magmas, are fully described ; and the 

 bearing of these facts upon the problems of vulcanology 

 are clearly pointed out. English readers will be pleased 

 to find a German treatise in which " Elevation-craters " 

 have finally disappeared, and scarcely less gratified to 

 read our author's conviction, very clearly expressed, that 

 the modified characters of the older lavas, as well as the 

 apparent deficiency of volcanic products among the older 

 geological formations, are due to secondary changes, and 

 that there is no real ground for the supposed absence of 

 granitic rocks among the igneous products of the younger 

 geological periods. We are glad, too, to notice that Dr. 

 Reyer recognizes the value and importance of the obser- 

 vations of Scrope and Darwin upon the banded structure 

 produced in viscid lavas ; though we think he fails to 

 appreciate the full bearing of these facts when he after- 

 wards proceeds to discuss the important question of the 

 origin of foliation. 



In the discussion of the problems connected with the 

 folding and faulting of rock-masses, during mountain- 

 making, Dr. Reyer exhibits the fullest knowledge and 

 impartiality. To the labours of Henry Rogers and other 

 American geologists, who nearly fifty years ago worked 

 out the structure of the Appalachians with such remark- 

 able skill and geological insight, he renders full justice, 

 and not less to the observations of their able successors 

 who have in recent years shown what singular variations 

 from the normal structure of mountain masses exist in 

 the Western Territories of their country. It is a fortunate 

 circumstance that the eastern and western portions of the 

 United States should present such perfect examples of 

 the diverse structures found in mountain ranges, and that 

 the geologists of that country have proved themselves so 

 capable of dealing with the grand but difficult problems 

 presented for their study. But at the same time our 

 author has fully set forth the value of the researches of 

 Lory, Baltzer, Heim, and others, who have shown that 



