92 REVIEWS 



grounds. Dr. Leith states squarely that isostasy and rigidity in any 

 high degree are mutually exclusive and as between the two he favors 

 rigidity. The rigidity of the earth is a matter whose importance has 

 been very generally passed over lightly, or carelessly swept aside by 

 students of mountain building. But the brilliant determination of 

 earth rigidity now in progress by Michelson, Gale, and Moulton firmly 

 establishes the view favored by the author. The results seem indeed 

 already to foreshadow that rigidity is the rock upon which not a few 

 favorite theories are destined to be wrecked. 



The average reader will perhaps be struck with the absence of num- 

 bered chapters. The framework of the book is really a skeleton outline — ■ 

 the familiar blackboard device of the systematic lecturer — ^with a few 

 principal headings, under which are marshaled a graded series of sub- 

 headings. The relative importance and correlation of these are rendered 

 easy by different styles of type. For systematic study as well as class- 

 room presentation this method has its advantages. 



The treatment is strong and judicial; the discussion closely woven 

 and effective, and while conciseness and brevity were doubtless sought, 

 they result in very concentrated nourishment. The reviewer is of the 

 opinion that the average working geologist will wish that the book 

 were about twice as long. The treatise is a distinctly valuable contribu- 

 tion. It has no equal in its field. 



R. T. C. 



The Devonian and Mississippian Formations of Northeastern Ohio. 

 By Charles S. Prosser. Geological Survey of Ohio, 4th 

 Ser., Bulletin No. 15. Pp. ix+574, 33 plates. Columbus 

 (1912), 1913. 

 The author devotes five chapters, or a major part of the bulletin, 

 to a detailed description and discussion of the more important rock 

 sections exposed in northeastern Ohio, together with observations on the 

 fossils usually found associated therewith, and to a review of the litera- 

 ture bearing on the geology of that section of the state. This is followed 

 by a chapter on correlation, and the bulletin concludes with the descrip- 

 tion and illustration of the major part of the Chagrin fauna, in which are 

 included four new species and two new varieties. 



The sections alone are a valuable addition to our knowledge of the 

 geology of that region, as they bring out clearly the varying character 

 of the rocks which have usually been classed together as a single forma- 



