ENERGY REQUIRED FOR MECHANICAL SLICING. 769 



COMPAEATIVE ENERGY REQUIRED FOR DEFORMATION IN ZONES OF 

 KATAMORPHISM AND ANAMORPHISM. 



The question of the amount of energy required to produce deformation 

 in the zone of katamorphism, in the intermediate zone, and in the deep- 

 seated zone of anamorphism is of great importance. 



The energy for rock deformation may be divided into two parts — 

 energy for mechanical work and energy for chemical work. The mechan- 

 ical work is of three kinds — the subdivision of the rocks, the transfer of the 

 material in order to produce a changed form, and the friction between the 

 parts of the subdivided rocks during the transfer. 



The most useful comparison as to the amount of energy spent in the 

 different zones is upon the basis of average mass deformation. By average 

 mass deformations I mean the strains necessary to change the shape of unit 

 masses of rock in a nearly similar way, so that the exterior forms are prac- 

 tically the same. To illustrate; 

 A cubic foot of rock may be sup- 

 posed to be divided into ten hori- 

 zontal slices and sheared parallel 

 to these slices, so as to produce, 

 ig-noring- the minor corners, a 



to <= Fig. 21.— Illustrating mass deformation of a rock. 



roughly rhomboidal mass (fig. 



21). If instead of ten there were a hundred slices, the approximation 

 to a rhomboidal mass would be closer; if a thousand, closer still; and so 

 on, until the slices became of infinitesimal thickness, when the mass would 

 be rhomboidal. In all of these strains the mass deformation averages about 

 the same. 



It is perfectly clear in the case of this hypothetical deformation that 

 the amount of work in rupturing is directly as the number of slices. The 

 average mass deformation is substantially the same, and the energy required 

 for chaiige of form — in other words, for transfer of material — is nearly 

 constant. The total amount of differential movement or shear is practically 

 the same in all cases, and therefore the friction is nearly constant. Hence, 

 in the case of the illustration, the energy for the deformation is almost 

 directly as the number of slices. But in the case of the crust of the earth, 

 supposing the fracturing to become closer as depth increases, the energy 

 mon xlvii — 04 ±9 



