GEOLOGY OF THE WEST fOINT QUADRANGLE, NEW YORK 25 



Highlands and that has appeared so hopelessly confused to the 

 average observer. For example, it is no unusual thing to pass, 

 within a short distance, from simple typical granite to typical banded 

 gneisses and perfectly typical schists, and even to carbonate and lime 

 silicate streaks representing former limy beds, without being able to 

 draw a sharp line anywhere between the different portions. Such 

 changes take place not occasionally, but repeatedly in a most con- 

 fusing series of repetitions and variations. Then again a formation 

 that seems to be a simple granite will in a short distance, without 

 any apparent line of demarkation, pass into a rock of streaked struc- 

 ture which would, if seen alone, certainly be called a gneiss. If 

 specimens were taken from two such nearby outcrops, it would 

 scarcely be considered conceivable that the two could belong to the 

 same formation and yet frequently in the field, where every inch of 

 ground is exposed, there is no possible line of separation between 

 them. 



It thus happens that one becomes accustomed to including great 

 ranges of quality and structural habit and mineral make-up within 

 the bounds of a single field unit. If one were to attempt mapping 

 on any other basis than this in the Highlands of N-ew York, it could 

 not be done on any scale much smaller than the ground itself, 

 because some of these variations take place within distances of 

 inches instead of feet or rods. And in those formations which have 

 the most complicated history, differences in quality occur by the 

 thousands in every conceivable method of arrangement, distribution 

 and repetition. 



It is necessary, therefore, to develop some method of generaliza- 

 tion as the only practical measure, and the best basis for this is 

 judged to be the origin and history. Units which have a definite 

 origin or an understandable sequence of development of variations 

 both within their own boundaries and upon their neighbors are 

 considered objects of special significance. All petrographic varia- 

 tions are referred to one or another of these units. It is readily 

 appreciated that generalization of this sort; leaves much to be 

 desired in the detail mapping and it is not assumed that mistakes 

 have been wholly avoided ; but it is the belief of the authors of this 

 bulletin that a large part of the complexities of the geology of the 

 Highlands may be made quite understandable on this basis. It 

 gives a better interpretation of the area than could be derived from 

 the most elaborate undertaking that tended to emphasize individual 

 differences rather than the larger and more fundamental similarities. 



