22 



NEW YORK STATE MUSEUM 



quartz crystals are also decidedly flattened parallel to the folia- 

 tion. The phenocrysts are embedded in a fine to medium-grained 

 matrix of feldspar, quartz, and biotite or hornblende. The rock 

 nearly always shows the effects of dynamic metamorphism, the 

 more or less crushed and granulated feldspars generally being 

 clearly visible to the naked eye. The degree of foliation often 

 varies considerably from place to place, and the porphyritic tex- 

 ture, especially along the borders, becomes notably less prominent. 

 The general range in mineral composition is shown by the 

 examples given in table 3. 



TABLE 3 

 Granite porphyry 









<u 





























+-> 



























1) 



ji 



(U 



«; 





0) 





u 













OQ 

 vt-t 





 d 







X, 

 



u 

 0, 



e 

 





 







Plagiocla 



N 



a 



3 

 Pi 





 W 







+3 



<u 

 C 



c ■ 

 

 

 ll 



1) 



"0 

 tS3 







a 

 < 



u 



c 













01-And 



















1 



25 



10 



10 



25 



I 



01-And 



44 



4 



4 



.... 



1 



4 



1 



2 



\ 



] 



2 



26 



10 



10 



25 



5 



30 



10 



.... 



I 



i 



1 



\ 



h 



.^ 



27 



15 



20 



20 



Ol-And' 



30 



8 





I 



1 

 4 



1 

 2 



1 

 4 



e 



^ 



28 



8 



35 



8 



7 



30 



.... 



10 



I 



1 

 4 



1 

 2 



1 

 4 





Number i is a very typical looking granite porphyry from the 

 quarry at Horicon., This is the rock which Professor Kemp de- 

 scribed as the *' Horicon gneiss " some years ago.^ 



Number 2 is from Kelm mountain ; no. 3 from one mile south of 

 Kelm mountain ; and no. 4 from the south base of Prospect 

 mountain. 



A good example of a rather coarse, somewhat porphyritic, pink 

 granite which might almost pass for a granite porphyry occurs ir 

 the c^uarry along the road 2 miles northeast of Pottersville. 



It so happened that no Grenville masses within the granite por| 

 phyry were of sufficient size to be indicated on the geologic ma] 

 but in the field one may see a good many small patches or streaki 

 of Grenville gneiss sometimes as clear-cut inclusions and at othet 

 times seemingly more or less fused into the granite, thus giving 

 very locally a sort of mixed gneiss effect. 



^ 17th Annual Rep't N. Y. State Geol. 1897, p. 510, 541. 



