GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK 65 



boundaries is faulted. It has no physiographic expression, as in the 

 Highlands all rocks have so nearly the same hardness that physio- 

 graphic features are usually the result of faulting and physical con- 

 dition rather than of original petrographic quality. 



Tihe rock is a light gray, medium to coarse-grained, acid granite 

 composed of quartz, white feldspar, striated and nonstriated, mus- 

 covite and biotite. The mica is not abundant and shows no signs 

 of orientation. 



In thin section it is a coarse-grained rock of granitoid structure. 

 The essential minerals are quartz, microcline, albite, orthorclase and 

 muscovite, with accessory biotite and epidote. The quartz and micro- 

 cline were the last minerals to form and the microcline contains 

 cores of the other feldspars. The epidote is a primary mineral and 

 is intergrown with the biotite and muscovite. The rock is fresh 

 except for slight kaolinization of the albite and bleaching of the 

 biotite, and it shows no signs of dynamic stress beyond an occasional 

 strained quartz grain or bent mica plate. 



Analysis 6847 Granite — Cornell 'dam (Peekskill granite) 



Si02. . 

 AI2O3. 

 FesOs. 

 FeO. . 

 MgO. 

 CaO.. 

 NazO. 

 KoO.. 



Norm. 



73 



54 



15 



20 





50 





81 





03 



I 



69 



4 



99 



2 



31 



1225 

 149 



3 

 II 



o 

 30 

 80 

 24 



Or. 



144 

 24 



24 



Ab. 



480 

 80 



80 



An. 



60 

 30 



30 



15 



Mgt. 



Hyp. 



Q. 



533 



Q 533 X 6c = 31.98 

 [Or 24 X 556 = 13.34 



F j Ab. 80 X 524 = 41 . 92 

 [An. 30 X 278 = 8.34 



Corundum 15 x 102 = 1.53 



Mgt. 3 x 232 = . 70 

 Hyp. 8 X 132 = 1 .06 



Femic. . .1 .76 



Salic . 



.97.11 



Sal. 

 Fern. 



32 

 — -^ 



64 " 



>. — = I Persalane 

 I 



Lassenose (I .4.2.4.) 



31 



- ■> - = Brittsnaire 



5 7 

 NaaO+KaO 104 7 5 



= <I - > - =^ Toscanase 



- CaO 30 I 3 



