REVIEWS 475 



and local phenomena and that although spectacular and ever interesting 

 to the popular mind, they are not entitled to the same space in such 

 a work as are the more general geologic processes. The main features 

 of vulcanism and volcanic rocks are, however, quite adequately treated 

 in the chapter on the composition of the earth, while volcanic moun- 

 tains as surface features appear in the very excellent chapter entitled 

 "The Great Relief Features of the Land." 



The proper handling of historical geology in brief space is a difficult 

 task. There is a great deal of ground to be covered and a great mass 

 of material to be judiciously picked over. Unless the work is well 

 done, the residue left is apt to be a dry bone skeleton with the flesh 

 and blood largely gone. In the historical portion of this work the 

 salient and vital points are made to stand out clearly. This is particu- 

 larly true of the life history. In part this is secured by a sprightly use 

 of paragraph headings to feature the various vicissitudes through which 

 life forms have passed in their long history. With these in mind, the 

 significance of the discussion is more readily grasped and the details 

 are more easily retained. 



The authors have treated the Tertiary as a "Period," giving it 

 the same rank in the geologic time scale as they do the Comanche or 

 the Cretaceous. After stating that it is divided into the Eocene, Mio- 

 cene, and Pliocene epochs, the Tertiary is discussed largely as a unit. 

 The Tertiary presents many rich problems for advanced students, 

 especially its mammalian evolution and its diastrophism, but these 

 are perhaps beyond the reach of a beginning class. The authors, believ- 

 ing that the points of newness or striking facts are largely over by the 

 time the Tertiary is reached, have apparently thought it best to curtail 

 the treatment and advance rapidly to the close of the history. 



A feature which cannot be too highly commended is the extensive 

 use of three-dimension diagrams to portray the operation of geologic 

 processes. This, in the reviewer's opinion, is much more expressive 

 than the ordinary style. The set of three block diagrams on p. 146 

 which picture the successive development of youthful, mature, and old 

 topography, illustrating not only the surface development of the streams 

 but the simultaneous lowering of the land toward peneplanation, shows 

 the possibilities of the method. 



By reducing the size of the illustrations, a very large number have 

 been successfully introduced and add very greatly to the effectiveness 

 and attractiveness of the book. It is a veritable picture book with 

 most of the pictures new to geologic readers. 



