GEOLOGY OF LAKE PLEASANT QUADRANGLE 



21 



separate representation of these transitional rocks upon the geologic 

 map. Within these areas there are occasionally narrow bands or 

 masses of normal syenite or granite approximately parallel to the 

 foliation, but no attempt has been made to show them upon the 

 map. As nearly as can be judged, this granitic syenite occupies 

 between 35 and 40 square miles of the area of the quadrangle. 



Mineralogically, the higher quartz content; frequent presence of 

 microcline ; invariable presence of biotite ; and general absence of 

 pyroxene characterize the granitic syenite as opposed to the normal 

 syenite. When the quartz content runs higher than 25 per cent, 

 the rock is classed with the granite. 



The rock shows practically the same textural and structural fea- 

 tures as those of the normal syenite. 



In addition to color variations like those of the normal syenite, 

 the granitic syenite often has a pinkish-gray to reddish color which 

 apparently is not always confined to the mere weathered surface. 

 Regarding the granitic syenite of the Long Lake quadrangle, Pro- 

 fessor Gushing says : ^ " Much of the rock is alternately green and 

 red, quite quartzose, and a rock distinctly intermediate between 

 syenite and granite, often passing into granite. Much of it is uni- 

 formly red, and the red rock ranges from syenite to granite in com- 

 position." These statements apply equally well to the region here 

 under consideration. 



A single rock ledge, i mile due southeast of the summit of 

 Hamilton mountain, furnishes interesting evidence regarding the 

 intimate relationships of dioritic, granitic, syenitic, and Grenville 

 gneisses. All these rock types are clearly exhibited in this ledge 

 about 40 feet across and their compositions, except the Grenville, are 

 shown in the accompanying table: 







(U 























1 







'-5 



1 









i 













53 



■| 



2 

 



5 



a 









1 

 >> 



1 



1^ 



2 

 1 



■5 



H 



24 



s 





55 



13 



7 



IS 





J 



I 



little 





23 



45 





23 



22 



3 





5 



I^ 



^ 



little 





21 



25 



38 



S 



27 



8 







I 



i 



Httle 











No. 24 is a rather basic (dioritic) rock greatly resembling certain 

 phases of the basic syenite; no. 23 is a granitic syenite; and no. 



IX. Y. State Mus. Bui. 115, p. 478. 



