Studies for Students. 



THE MAPPING OF THE CRYSTALLINE SCHISTS. 1 



II. BASAL ASSUMPTIONS. 

 Introduction. 



Deformation under compressive stresses either by flow or by rupture. 

 Deformation zones of the lithosphere. 

 Mechanics of deformation by flow. 

 Mechanics of deformation by rupture. 

 Systems of faults. 



Direct genetic relations of joint systems to systems of normal faults. 

 Criteria for recognizing a system of folds. 



Criteria for recognizing a combined system of joints and faults. 

 Key areas for determining manner of deformation of a region. 

 Nature of evidence for establishing a fault. 

 Nature of evidence for establishing a system of faults. 



Method of mapping an area deformed by a system of folds in conjunction with a 

 system of faults. 



INTRODUCTION. 



In an earlier paper bearing this general title 2 the writer has 

 discussed the methods of mapping the crystalline schists, and 

 taken occasion to emphasize the necessity for a larger use of 

 outcrop maps for all complexly deformed areas. It was also 

 advocated that many peculiarities of rock exposures besides 

 those ordinarily observed be examined and recorded, and their 

 significance be sought in the final interpretation — the drawing 

 of boundaries and the coloring of the map. In the present 

 paper it is proposed to go somewhat deeper into the subject, 

 and to discuss the basal and perhaps unconscious assumptions 

 of the geologist in the making of his map. 



If the writer's contention is upheld, it will be shown that 

 methods of mapping have not kept pace with the advance of 



1 Published with the permission of the director of the United States Geological 

 Survey. 



*Tour. Geol., Vol. X, 1902, pp. 780-92. 



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