52 NEW YORK STATE MUSEUM 



Spar as the dominant constituents. The occurrence of pegmatitic 

 facies is judged to support the interpretation given that igneous 

 injection and impregnation of the original Grenville sediments by' 

 a magma of dioritic composition has been responsible for all of 

 these effects. In some places it varies even to the composition of 

 a soda granite. 



In its simplest form, however, the rock presents the appearance 

 of a somewhat modified diorite, medium to somewhat basic plagio- 

 clase is prominent, augite and hornblende are usually both present 

 and the other constituents vary greatly. 



Generally the relation of this igneous member to other igneous 

 representatives is obscure. The somewhat more intimate penetra- 

 tion of the diorite and the comparatively clear-cut relation that cer- 

 tain of the granites bear to this diorite gneiss supports the con- 

 clusion that the diorite invasion was the earliest of all (see mixed 

 types, p. 57, for additional detail). 



Canada Hill granite. The Canada Hill granite, as exposed 

 typically at Kings quarry south of Garrison, is a medium gray, 

 medium-grained rock varying from faintly to very perceptibly 

 streaked. It is composed of white and gray feldspar, gray quartz, 

 small crudely oriented biotite crystals, and numerous small, rounded, 

 violet-red garnets. 



There is also a pegmatitic facies which is coarser-grained, grading 

 into true pegmatite. It is penetrated by or streaked with white 

 segregations of quartz and feldspar, resembling alaskite, carrying 

 large patches of red-brown garnet aggregate. 



The weathered surface is dull gray. The feldspar and biotite 

 weather out leaving the quartz and garnet. The new fracture in 

 the weathered rock has a faintly pinkish or yellowish tinge. The 

 mica is bleached yellow and carries rutile, the feldspar is rather 

 chalky, and the gray quartz and dull-red garnets stand out clearly. 



This type represents the oldest and most vigorous of the granite 

 magmas which have invaded the ancient complex of this district. 

 Microscopically the rock varies greatly. On the whole, however, it 

 is medium grained with remnants of dusty looking orthoclase as a 

 prominent constituent with much fresher looking microcline with 

 soda feldspar comparatively common, and abundant reddish brown 

 biotites carrying numerous oriented rutile needles. Quartz also is 

 a prominent constituent. 



A characteristic appearance and composition is shown by no. 440 

 (plates II and 12). 



