12 NEW YORK STATE MUSEUM 



South of the Glenham belt, in the town of Matteawan, are two 

 smaller inliers of the gneisses connecting the Glenham belt with 

 the Highlands. 



Between the rocks of the Highlands and those composing the 

 masses of inliers there are some differences which help to throw 

 light on the history of both. There are also marked resemblances 

 which apparently serve to clinch their relationship. 



PROBLEM OF THE GNEISSES 



The study of the gneisses speedily develops very puzzling prob- 

 lems, which in all cases may not admit of satisfactory solution. In 

 some way these rocks must express the several successive changes 

 which they have experienced. A complex history is suggested, but 

 all its events are not easy to trace. 



PROMINENT STRUCTURAL FEATURES 



The most impressive feature of the gneisses is the northeast- 

 southwest alignment of the ridges which constitute their outcrop. 

 Between the ridges are parallel longitudinal valleys. From the 

 published descriptions, these features, with some exceptions, seem 

 to hold for the entire Highlands and to extend southward into West- 

 chester county. 



The gneisses are uniformly banded or foliated throughout their 

 entire breadth from west to east, and the strike of the foliations 

 in general follows the trend of the ridges. In a few places only 

 does the foliation approximate schistosity in any degree. 



Over most of the area there is an easily distinguishable arrange- 

 ment in parallel stratalike masses which also follow the topo- 

 graphic features. These do not show an orderly repetition, though 

 masses of very similar mineralogy are irregularly repeated. Occa- 

 sionally more massive types occur, but these, too, seem to follow the 

 structural features just mentioned. The prevailing dip of the folia- 

 tion planes to the southeast imparts a strongly isoclinal character. 



The ridges clearly date from Postcambric time. It seems rea- 

 sonable to infer that the other structural features just outlined 

 have a common origin and belong to an earlier epoch. 



There is much evidence of extensive faulting which is developed 

 chiefly, or at least most prominently, along the strike. Such faulting 

 might easily account for the lack of orderly repetition of character- 

 istic rock types. Most of this faulting belongs to the disturbance 



