RELATIONS OF ZONES. 767 



belt, we may consider the metamorphism of an imaginary rock of homo- 

 geneous character, composed of a single mineral which extends from the 

 surface to an indefinite depth. Near the surface the rock is broken into 

 blocks by faults and joints. There is no marked deformation of the indi- 

 vidual particles, except in thin layers along the fractures. The textures of 

 the rocks are for the most part preserved. Deeper down the fractures are 

 closer together, and at sufficient depth the layers may be no thicker than 

 leaves. Still deeper down every particle takes part in the deformation. 

 This is the belt in which granulation is prominent, although with it there 

 may be some recrystallization. Still deeper down recrystallization becomes 

 important, and finally dominant. In the intermediate belt fracture and 

 no wage do not exclude each other; both occur to varying extent in different 

 positions at the same time. 



The transition above described for a single formation composed of a 

 single mineral takes place at different depths for different formations and 

 for different minerals of the same formation, and hence it is that in hetero- 

 geneous formations all the phenomena discussed under both the zone of 

 katamorphism and the zone of anamorphism may occur together. 



At a given depth the stronger or less readily recrystallized rocks may 

 be largely deformed by fracture, and the weaker or more readily recrystal- 

 lized rocks be largely deformed by flowage. The result is that original 

 textures and structures may be more or less preserved in the former, while 

 in the adjacent layers original textures and structures may be entirely 

 destroyed and the rocks become slates or schists. It very often happens 

 that the alternating beds which show original textures and structures and 

 those in which they are obliterated are not more than a few inches thick. 



In the intermediate belt many of the beds are deformed by combined 

 mass fractures and fractures of the individual mineral particles, so that in the 

 same rock in which joints, faults, fissility, etc., and the alterations attending 

 these phenomena occur, there are also found, between the major fractures, 

 all grades of deformation by interior movement, from the earliest stages of 

 peripheral granulation of the grains to complete granulation or recrystal- 

 lization, extending throughout the mineral particles. Thus we have all com- 

 binations of macroscopic and microscopic fractures and recrystallization. 



In some places the intermediate belt is broad; in other places it is 

 narrow. The phenomena of the belt may be seen in aqueous and igneous 

 rocks alike. Many illustrations of each might be given. 



