MAPPING OF THE CRYSTALLINE SCHISTS 87 1 



the eye again sees the runic characters, and it depends only upon this, that 

 they all be correctly understood in the future. 1 



The observation of these striking lineaments of the surface, 

 however, unless they be of great perfection, hardly furnishes an 

 adequate demonstration that an important deformation by fault- 

 ing has occurred. The proof of this must rest upon the dis- 

 covery of a considerable number of individual faults whose 

 directions relegate them to a system of parallel and intersecting 

 series. The methods by which individual faults may be recog- 

 nized will be outlined in the sequel. 



KEY AREAS FOR DETERMINING THE MANNER OF DEFORMATION OF 



A REGION. 



In geological mapping it is almost an unwritten law that 

 geological sequences must be established at points where forma- 

 tions appear in their larger masses at the surface, it being 

 assumed that structural relations are in such cases the simpler. 

 Areas which show a considerable number of formations brought 

 closely together in small masses at the surface are looked upon 

 with suspicion as areas of local and "minor" faulting, or as con- 

 taining intercalated beds of unusual types due to purely local 

 conditions of sedimentation. Whichever of these views is 

 assumed, the areas are likely to receive but small attention ; 

 first, because the problem of their structure is difficult to unravel 

 and not regarded as affecting the larger questions of the region ; 

 and, second, because if once unraveled, the scale of the map 

 would not allow of its representation. Such areas are, therefore, 

 most frequently represented upon the map in the color of the 

 formation which is believed to compose their greater part. 



However unsuited these intricate areas may be supposed to 

 be for establishing the order of succession of geological forma- 

 tions, they are nevertheless, it is believed, in many cases the 

 keys (and perhaps the only ones) to unlock the secret of the 

 manner of deformation which has affected the area as a whole. 

 Complicated indeed, they often require only patience and 

 industry for their unraveling, whereas the larger masses by their 



1 Op. cit., p. 334. 



