DEFORMATION OF THE LITHOSPHERE. 1005 



CLASSIFICATION OF ORE DEPOSITS. 



Ore deposits may be divided into three classes upon the same basis as 

 are the three great divisions of rocks: 



(1) Ores produced by the processes of sedimentation, or sedimentary 

 ores. 



(2) Ores produced by igneous processes, or igneous ores. 



(3) Ores produced by the processes of metamorphism, or metamorphic 

 ores. 



Since this volume is a treatise upon metamorphism and not upon 

 physical geology in general, only the third class of ores, those produced 

 by metamorphism, come within its scope. But ores formed by processes of 

 sedimentation and by igneous processes will be briefly considered, mainly 

 in order to point out their relations to ores produced by processes of 

 metamorphism. 



Before taking up the ores it is necessary, as already stated, to summarize 

 certain parts of the previous chapters. The three great divisions of the 

 processes of modifications of rocks which most intimately concern ore 

 deposits, and therefore need to be summarized, are: 



The deformation of the lithosphere. 



Volcanism. 



The circulation and work of solutions. 



DEFORMATION OF THE EITHOSPHERE. 



In another place I have shown that the outer part of the crust of the 

 earth may be divided into three zones, depending upon the character of the 

 deformation — (1) an upper zone of rock fracture, (2) a middle zone of 

 combined rock fracture and flowage, and (3) a lower zone of rock flowage. a 

 In Chapter IV it has been shown that the zone of fracture corresponds to 

 the zone of katamorphism and that the zone of flowage corresponds to the 

 zone of anamorphism. 



ZONE OF FRACTURE, OR ZONE OF KATAMORPHISM. 



The zone of fracture is that near the surface and in it the rocks are 

 deformed mainly by macroscopic fracture. The ruptures are those of 

 faulting, jointing, bedding parting, fissility, and brecciation. The rocks 



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

 IT. S. Geol. Survey, pt. 1, 1896, p. 589. 



