GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK 6l 



In places also pegmatitic injection effects are very prominent indeed 

 and the rock is charged more or less with f eldspathic and quartzose 

 matters of this origin, so that it is much more complex in composi- 

 tion at these places than is normal for the simple metamorphosed 

 rock. 



More rarely other minerals are prominent, such as sillimanite, 

 graphite, carbonate, sulphide, feldspar, tourmaline and garnet, but 

 these are not by any means uniform and some are comparatively rare. 

 The most widely distributed of this lot of constituents probably is 

 garnet, which seems to be a regional metamorphic in origin. It is 

 very generally and abundantly distributed in this formation. 



The rock is always foliated and sometimes streaked, but never 

 banded. It is in many places crumpled in a very complex way, but 

 this is not a universal effect. It is more likely to be streaked in 

 connection with pegmatitic development and it is very seldom indeed 

 that one can find any evidence whatever of original bedding, although 

 the general structural trend and the limestone contact as well as 

 certain sill-like meta diabases (hornblende schist bands) give some 

 general idea of the formational attitude. 



The average microscopic appearance is illustrated by photomicro- 

 graphs (plates 34, 35 and 36). 



Analysis of Manhattan Schist 

 Composite of five specimens from the borders of the Cortland t 

 series, representing the different types. One is chiefly garnet, quartz 

 and mica; the others carry considerable feldspar, along with the 

 quartz and mica. 



SiO. 57.94 Mode Recast 



AUOs 21.70 Qtz. 19.20 



Fe^Os 1.57 Or. 5.56 



?n ^"^ f- ^4-^7| Flag. = Alb. 



MgO 2.49 An. 2.5o( * 



CaO .50 Muscov. 38.01 



NaaO 1.74 Biot. 14.86 



K2O 4.68 Mgt. .70 



H2O-H 2.17 Ilmen. 1.85 



H2O— .29 



P=05 tr 97.35 



TiOs 1. 01 == 



MnO .19 



100.18 



Analysis and recast by G. Sherburn Rogers. 



