GEOLOGY OF THE BLUE MOUNTAIN QUADRANGLE 2/ 



between 20 and 25 per cent. So far as could be determined in the 

 field, this granitic syenite is intermediate between the normal syenite 

 and the granite, always grading into one or the other or both. 

 Nothing like definite evidence was obtained to show that any one 

 of these rock types cuts another. Though any attempt separately 

 to delimit the granitic syenite on the geologic map must be rather 

 arbitrary, it is believed that, as a result of careful attention to 

 the matter in the field and the study of thin sections, the areal 

 relation of the granitic syenite to the normal syenite and the 

 granite are fairly well brought out. 



• This granitic syenite occupies nearly one-third of the area of the 

 quadrangle and, like the normal syenite, is widely distributed in 

 ver}^ irregular shaped bodies. 



Much of the rock shows the usual color of the normal syenite, but 

 pinkish to reddish granitic syenite is not uncommon, thus suggest- 

 ing the typical granite into which it grades. 



Texturally and structurally the granitic syenite shows essentially 

 the same sorts of variations as the normal syenite. 



Mineralogically the granitic syenite differs from the normal 

 syenite chiefly in the larger content of quartz, somewhat smaller 

 content of plagioclase, and absence of pyroxene. 



In table 5 the compositions of a number of thin sections of granitic 

 syenite are shown. 



Granite 



About 15 square miles of the quadrangle are separately mapped 

 as granite, but, since this rock is abundantly represented in most 

 of the mixed gneiss areas, the actual extent must be increased to 

 something like 25 square miles. No field evidence was found to 

 show that any of the granite is distinctly older or younger than 

 the syenite or granitic syenite, though in many places perfect 

 gradations from one to another were observed. 



The granite facies vary in color from light gray or greenish gray 

 to pinkish gray or Hght red. In some cases the reddish color is a 

 mere surface weathering effect as, for instance, on the eastern 

 face of Waterbarrel mountain where, within i or 2 feet, a super- 

 ficial pink color passes downward into a light brown, and finally 

 into a greenish gray color Avhere the rock is very fresh. In other 

 cases the reddish color permeates the rock to depths of 10 or 20 

 feet as is well exhibited in the quarry on the road 25^ miles east 

 of Long Lake village. In still other places the pinkish or reddish 

 color seems to be the inherent color of the rock or, if due to 



