866 STUDIES FCR STUDENTS 



mosaic type of infaulted structure seems to have been restricted 

 to papers upon the Great Basin of the West and upon areas of 

 Newark rocks along the Atlantic border, in both of which 

 provinces only the simplest types of folding are observable. It 

 is highly probable that joints and "minor faults" have been 

 elsewhere frequently observed but thought to have throws so 

 small as to be negligible, the cumulative effects of the small 

 displacements along numerous near-lying planes being over- 

 looked. Faults have too frequently been regarded as isolated 

 phenomena. Within the crystalline areas isolated normal 

 faults have sometimes been supposed to stand in some relation 

 to folds, and because evidence of individual faults is within such 

 areas most difficult to secure, faults have been the last resort of 

 mappers in securing harmony between areal relations and basal 

 hypotheses. The tendency to use faults "to get out of tight 

 places " has probably been in direct ratio to the inadequacy 

 of the hypotheses assumed, and it is, therefore, not strange 

 that faults have been and still are in much disfavor among the 

 most competent and conscientious of American geologists. 

 There are, however, as the writer believes, methods of showing 

 the connection of a system of faults with the deformation of an 

 area, through the peculiarities of its joint system, topography, 

 hydrography, outcrop distribution, etc. 



It will be the object of this paper to point out especially 

 the methods of recognizing fault systems when in conjunction 

 with systems of folds, because in the manner of deformation of 

 an area is involved the most fundamental assumptions of 

 geological mapping. The view that important deformation 

 may be brought about within a folded area of the crystalline 

 schists by a system of normal faults, has hardly been discussed 

 by American geologists, the system of folds being invariably 

 present and supposed to be the only important manner of 

 deformation exhibited. 



The impression should not be gained that in the mind of the 

 writer the relative importance of the two methods of deforma- 

 tion is correctly set forth by the space here devoted to each. 

 Deformation by folding is comparatively well understood and 



