DEFORMATION IN ZONE OF FLOWAGE. 1011 



From the above it appears that openings of the zone of the combined 

 fracture and flowage comprise all of the classes of openings characteristic of 

 the zone of fracture. There is, however, the great difference that upon the 

 average the supercapillary openings are smaller, less continuous, and less 

 numerous than in the zone of fracture. 



Since there is such a great variation in the strength of the rocks and in 

 other factors, the belt of combined fracture and flowage may be of consid- 

 erable thickness, possibly as thick as 5,000 meters. In this zone we have 

 all combinations of the phenomena of fracture in the various ways above 

 mentioned, and of flowage by granulation and recrystallization. 



ZONE OF FLOWAGE, OR ZONE OF ANAMORPHISM. 



In tne zone of rock flowage deformation is chiefly by granulation and 

 recrystallization, few openings being produced, except those of microscopic 

 size. (See pp. 658-659, 673-675, 685 et-seq.) This conclusion rests upon 

 arguments which can not here be fully repeated." However, it may be 

 said in passing that the conclusion that a zone of rock flowage exists at 

 moderate depth is based, first, upon deduction from known physical 

 principles as to the behavior of solid bodies under pressure; and, second, 

 upon observation. It is well known that when a rigid body, such as a rock, 

 is subjected to unequal stresses in various directions and the difference in 

 the stresses is greater than its ultimate strength under the conditions in 

 which it exists, it must rupture or flow. If a rock be subjected to a 

 stress in a single direction greater than its ultimate strength in that 

 direction, and the rock is not under pressure in other directions, rupture 

 occurs. However, if we suppose that the rock be subjected to stresses 

 greater than the ultimate strength of the rock in all directions, and that 

 the difference in the stresses in different directions is greater than the 

 ultimate strength of the rock under the conditions in which it exists, then 

 if openings could be produced by rupture, they would be closed by 

 pressure. In other words, at a certain depth below the surface of the 

 earth, if we could suppose that cracks and crevices are formed by the 

 deformation to which the rocks are subjected, the pressures in all directions 

 being greater than the ultimate strength of the rock, these cracks and 



«Van Hise, C. R., Principles of North American pre-Cambrian geology: Sixteenth Ann. Rept. 

 U. S. Geol. Survey, pt. 1, 1896, p. 594 et seq. 



