746 REVIEWS 



Chap. 7 treats of the beh of cementation. This bek is defined as extend- 

 ing from the belt of weathering to the bottom of the zone of fracture. The 

 geological results are found to contrast very markedly with those of the belt 

 of weathering. In the latter belt solution is the rule; openings are enlarged; 

 the rocks degenerate. In the belt of cementation, on the other hand, the 

 processes of metamorphism continuously deposit material, the openings 

 are closed, and thus the rocks are consolidated. Each of the cementing 

 substances is considered, and an explanation is offered as to why cementa- 

 tion rather than solution is a general process in this belt. 



Chap. 8 treats of the zone of anamorphism. This is the zone in which 

 rock flow occurs. Full explanations of the meaning of rock flow and of 

 the development of such secondary structures as slatiness, schistosity, and 

 gneissosity are offered. Perhaps the most important generalization is that 

 rock flow is mainly accomplished through continuous solution and deposition, 

 that is, by recrystallization of the rocks through the agency of the contained water. 

 But rock flow is partly accomplished by direct mechanical strains. At the begin- 

 ning of the process, during the process, and at the end of the process, the rocks, 

 with the exception of an inappreciable amount, are crystallized solids. 



Chap. 9 treats of rocks. A classification of the sedimentary rocks is 

 given, their genesis is discussed, and the series of transformations through 

 which each of the rocks passes is traced out, the resultant rocks being indi- 

 cated. It was not found possible to give a similar treatment for the igneous 

 rocks. 



With the ninth chapter the subject of metamorphism proper closes, but 

 the results contained in these nine chapters have an important bearing upon 

 other parts of physical geology. The remaining chapters consider these 

 relations. 



Chap. lo discusses the relations of metamorphism to stratigraphy. It 

 is shown that in consequence of metamorphism great difficulties are intro- 

 duced in stratigraphical work. The nature of the difficulties and the 

 manner in which they may be overcome are fully considered. 



Chap. II treats of the relations of metamorphism to the distribution of 

 the chemical elements. This is perhaps the most daring of the various 

 attempts at generalizing of the treatise. It is shown that as a result of the 

 forces and agents of metamorphism the elements of the original igneous 

 rocks are redistributed, a given element being less abundant in the larger 

 number of sedimentary rocks than in the original rocks, and corresponding 

 with this depletion each of the elements is segregated in one or more forma- 

 tions. An attempt is made to treat the problem of the redistribution of the 

 elements quantitatively. Assumptions are made as to the total mass of the 



