■660 



SCIENCE. 



[N. S. Vol. V. No. 12f. 



which the study is hegun." The chapters 

 themselves, however, treat of the subjects 

 with precision and sufficient detail for the pro- 

 duction of definite notions on the points dis- 

 cussed. 



The treatment of Historical Geology is on 

 the lines of Dana's Manual, but without the 

 details. This method in an exhaustive manual 

 is valuable, but it may be doubted whether the 

 use of so many scientific names of animals and 

 plants as is necessary in such a treatment con- 

 veys any definite information to readers who 

 are unfamiliar with zoology and botany ; and 

 even to zoologists, unless very well acquainted 

 with the paleontological side of their science. 

 The fact is that a really satisfactory mode of 

 treatment of this fascinating subject of the 

 biological problems of historical geology has 

 not yet come to light. 



The illustrations are, in the main, excellent 

 and new and, as has been said, richly Ameri- 

 can. But some of them are so imperfectly re- 

 produced from the original photographs as to 

 lose much of their value. 



The publishers' part of the work is well done, 

 though the user of the book will often be caused 

 to lament that it is found necessary to put so 

 much weight into a book one is expected to 

 hold in a single hand. 



H. S. Williams. 



Yalk University. 



The Glaciers of North America. By Israel C. 

 Russell, Professor of Geology in the Uni- 

 versity of Michigan. Boston, Ginn & Co. 

 Pp. x+210. 



When the glaciers of Switzerland had been 

 well explored those in this country were 

 scarcely known, and now Professor Kussell tells 

 us that North America is the best region in the 

 world for the study of glaciers ; that all types 

 occur here, of all sizes and in great variety ; 

 and he makes good his assertion by the descrip- 

 tions of the glaciers of North America, so far as 

 they are now known, which fill the greater part 

 of the volume before us. 



Professor Russell attacks his subject as a 

 geographer ; his aim is to report the present 

 condition of knowledge concerning the glaciers 

 of this country and to ' stimulate a thirst for 



fresh explorations and renewed study along an 

 almost untrodden path.' 



To carry out this object the book must neces- 

 sarilj' be largely a compilation, but the material 

 for an important part is furnished by the original 

 papers of the author himself Of these we 

 mention especially the account of the Mt. St. 

 Elias region, which Professor Russell explored 

 in the course of two remarkably plucky at- 

 tempts to ascend Mt. St. Elias. 



He opens with a chapter giving a clear ac- 

 count of the characteristics of glaciers and their 

 work, in the course of which he is confronted 

 with the question : ' What is a glacier ?' 



A concise definition of a class of natural ob- 

 jects is always difficult ; and certainly none 

 has yet been given which includes all the 

 phenomena of glaciers. Mr. Russell recognizes 

 this and gives provisionally the following defi- 

 nition : A glacier is an ice body originating from 

 the condensation of snow in regions where 

 secular accumulation exceeds melting and evap- 

 oration, i. e., above the snow line, and flowing 

 to regions where waste exceeds supply, i. e., 

 below the snow line. 



The majority of geologists and physicists 

 would accept this as fairly representing the 

 essential characteristics of a glacier ; but the 

 small number who believe that the force urging 

 a glacier down its bed is not due to gravity 

 alone, but to a large extent to the increase of 

 the volume of the ice on account of the growth 

 of the ice grains, must utterly reject it ; for, 

 according to their hypothesis, the source of 

 supply is not snow that falls in the n6ve-fields, 

 but the water that freezes throughout the body 

 of the glacier. 



The glaciers of North America are confined 

 to the Cordilleran mountain series and to the 

 Greenland region. Professor Russell says that 

 ' ' the Cordilleran glaciers form an irregular 

 curve, broadest and reaching the sea line in 

 the Mt. St. Elias region, and narrowing and 

 becoming more and more elevated at both its 

 western and southern extremities, ' ' and then he 

 successively describes in greater detail the 

 glaciers of the Sierra Nevada ; of the Cascade 

 range, the higher peaks of which are volcanic 

 cones and carry glaciers radiating from their 

 summits ; of Canada, and of Alaska. The 



