252 Scientific Intelligence. 



phenomena of raetamorphism in order and to show how they are 

 throughout the expression of chemical and physical laws opera- 

 ting within the crust of the earth. 



The earliest stage of science is largely descriptive, qualitative 

 and speculative. The branch of metamorphic geology may now 

 be said to have fully passed through such a preliminary stage 

 and to have entered upon its final development. Although many 

 able works have appeared in the past this treatise must be looked 

 upon as the landmark of a new era, a starting point from which 

 further studies will largely take their departure. Following 

 these introductory statements the volume itself may be described. 



In the introductory chapter it is shown that a great difficulty 

 in studying metamorphism arises from the fact that many of the 

 changes take place under conditions which cannot be directly 

 observed, so that the forces and agents accomplishing certain 

 results must be inferred from the nature of the results. This 

 method is directly the opposite of that which has usually been 

 applied to the elucidation of surface geology, and this fact gives 

 the peculiar difficulty to the deeper problems of metamorphism 

 and has retarded its development to a period later than that of 

 any other branch of the science. 



Under metamorphism is embraced not only the changes which 

 take place in the deeper parts of the lithosphere but surface 

 alterations as well, so that the treatise covers a large part of the 

 ground of the older treatises on chemical and physical geology. 



It appears that the processes of metamorphism, using the term 

 in this inclusive manner, come under surprisingly few heads. 

 The upper zone, characterized by hydration, oxidation, carbona- 

 tion, resulting in expansion of volume and production of heat, 

 tends to break down complex mineral molecules into a few of 

 relatively simple composition and, following the analogy of the 

 term of katabolism in biology, the zone is called the zone of 

 katamorphism ("kata" meaning tearing down). This zone is 

 divided into a belt of vjeathering extending to the level of ground 

 water and below this a belt of cementation, within which is 

 deposited much of the silica and other substances carried down- 

 ward from the belt of weathering. 



The zone of katamorphism corresponds roughly with the zone 

 of fracture. Below this pressure due to gravity becomes the 

 dominant factor in reactions. Complex compounds whose for- 

 mation is attended by contraction of volume result from more 

 simple ones. The reactions are characterized by a tendency to 

 dehydration and decarbonation where water or carbonic acid is 

 present. Again, following the analogy from biology, this zone, in 

 which complex molecules are built up, is named the zone of 

 anamorphism (from " ana " meaning a " building up "), and cor- 

 responds in general with the zone of flowage, the one term 

 expressing the character of the chemical and mineralogical 

 changes, the other the character of the mass deformations. 



In both zones it is believed that the total reactions involve the 



