GEOLOGY OF THE BLUE MOUNTAIN QUADRANGLE 21 



and highly gneissoid. Within this anorthosite-gabbro there are 

 several inclusions of light gray Grenville gneiss up to 2 or 3 feet 

 wide, some bands of amphibolite and a few masses (one 25 feet 

 across) of granitic syenite, all of these being arranged approximately 

 parallel to the foliation of the inclosing rock where that structure 

 is present. Whether the granitic syenite occurs as inclusions or as 

 dikelike intrusions could not be positively determined, though they 

 are most likely the latter. 





Table 2 - 



-Thin-sections of anorthosite 



— gabbro 







Slide 

 Number 



6 • 



i 



cl 



1 



.^ 



s 



1 



^ 

 a 





S 



S 



g 



.■§ 



^ 



















a 







. a 





.tl 











s 



£ 



|UJ 



P 



w 



< 



a 







< 



SI 



ISl 



a. 



CQ 



U 



61 



176 5(0 

 176 5(d) 



an.-Lab. 

 an.-Lab. 



1 



63^ 35 



88 I 









I 

 T 







Httle 

 Uttle 



little 

 little 



little 









62 













little 





63 . . . 



176 5(e) 

 176 5(0 



an.-Lab. 





15 







3 



2 







i 





little 









64 



an.-Lab. 



77i 15 





I 





^ 



little 



little 



. 





65 



176 S(g) 



an.-Lab. 



80 16 







Httle 



T 







i 



i 







2 





66 



176 5(h) 

 176 9 



an.-Lab. 

 ol.-Lab. 



80. . . 









I 











Httle 

 Httle 







19 



58 



661 6 





2 



2 



12 



10 





Httle 















Nos. 61 to 66 inclusive are from the area on the eastern shore of Long lake ; 

 no. 58 is from the area west of Long lake and is more acidic than the usual 

 rock there. 



A number of small pegmatite dikes cut through the whole mass of 

 rock. There are no exposures of any kind immediately surround- 

 ing the anorthosite-gabbro area so that nothing could be learned 

 regarding its relation to the other rocks of the vicinity. 



Syenite and Its Facies 



The syenite and its basic and acidic facies are the most wide- 

 spread of all the rocks. As here considered they vary greatly, 

 ranging from what may be termed a normal quartz syenite to a 

 basic (dioritic to gabbroic) facies on one hand to granitic syenite 

 and granite on the other. Since these facies grade back and forth 

 into one another, sharp boundary hues between them do not exist 

 and their separation on the geologic map depends to a considerable 

 extent upon personal judgment based upon some years of experience 

 with the rock types and checked up by the study of numerous 

 thin sections. 



As is now well known, the syenite is younger than the Grenville 

 series and distinctly intruded into it, there often being dikelike 



