GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK 69 



serial relationship. It is probable that the latter (the pyroxenites) 

 were intruded first, followed closely by the norites so that sometimes 

 these varieties are found banded together in flowlike masses. The 

 diorites must have come next." 



STRUCTURAL GEOLOGY 



(Larger structural features) 



The larger structural features represented in the district are of 

 enough variety and complexity of origin to warrant discussion under 

 a separate head. These features may be grouped as follows : 



1 Internal structures of formations, especially those with igneous 



control or history. 



2 Form represented by the individual units shown on the map. 



3 Tectonic features or deformation structures. 



4 Metamorphic structures. 



Internal Structure Detail 



£he larger units belonging to the Precambrian all show a variety 

 of structural detail, the chief of which is a streakedness grading 

 into clear-cut banding on one side and into massive habit on the 

 other. This has already been referred to in its genetic bearing in 

 connection with petrogenesis. It is sufficient in this present con- 

 nection to emphasize the prominence of this feature, which charac- 

 terizes practically all the older units. It is a structure which is of 

 particular prominence in those belts where the Grenville sediments 

 are more or less in evidence, but is not by any means confined to 

 the Grenville limits. As already pointed out, the origin of much of 

 the structure is due to an actual mixing of types, so that a grada- 

 tional boundary rather than a sharp line division ought to be 

 expected and is commonly found. 



In spite of this fact, there are reasonably clearly defined large 

 field units, and their internal structural detail, however complicated, 

 must be considered of minor significance. 



In addition to the streakedness and the banding already noted, 

 there is xenolithic structure representing incorporated blocks of 

 older material as one extreme and also pegmatites representing final 

 stages of crystallization as the other. These two habits add further 

 to the irregularities and structural variety of formations. The total 

 result is the apparent structural confusion referred to in an earlier 

 chapter. As a matter of fact, these differences are not abnormal to 



