770 A TEEATISE ON METAMORPHISM. 



required for a given mass deformation would increase with depth for two 

 reasons: (1) More energy is required for the finer subdivision; and (2) the 

 load increases with depth, and therefore the energy required to overcome 

 friction also increases with depth. The energy required for the similar 

 transfers of material remains practically the same at all depths. 



It has already been seen that near the surface the dominant deforma- 

 tions are relatively wide-spaced faults and joints; that with increase of 

 depth the spacing between the faults and joints decreases until the fractur- 

 ing is that of fissility and finally of granulation. 



It is therefore clear that the amount of energy required for fractures 

 a considerable distance apart, such as prevail where faults or joints, or 

 both, are the dominant deformations, is much less than where the fractures 

 are close together — as, for instance, in fissility. Furthermore, it is clear 

 that the amount of energy required for the slicing of fissility is much less 

 than that required for granulation of the individual particles, for in the 

 latter case a mass equivalent to a fissile leaf must be broken into a 

 multitude of particles. Probably the ratio between the energy required 

 for breaking a rock into fault or joint blocks near the surface and that 

 required for producing fissile leaves deeper down is not greater than the 

 ratio between the energy required to produce fissility and that required to 

 produce granulation throughout at a still greater depth. No general ratio 

 between the amount of energy spent in deformation by faults and joints 

 and deformation by granulation can be given, but it is certain that the 

 amount of energy used in extreme cases of the latter may be indefinitely 

 greater than that required for the former. 



Since it is certain that in passing from the surface to considerable 

 depth there is a passage from deformation by faulting or jointing, or both, 

 to deformation by granulation, it is certain that to a depth of many hundred 

 meters there is a steady and very rapid increase in the amount of energy 

 required for a given mass deformation. 



At sufficient depth, as has been seen, granulation is more and more 

 replaced by recrystallization, and finally this process is dominant. It would 

 be very interesting to know exactly the relative amounts of energy required 

 for the two processes of granulation and recrystallization. 



As already noted, the energy required for granulation is wholly 

 mechanical, and includes three factors — (1) that required for the subdivision 



