ABSTRACTS OF PAPERS 



131 



Throughout the two areas much of the granite contains myriads of small, 

 nearly white lenses (inclusions) of quartz-sillimanite schist. These lenses, 

 which are of all sizes up to iy 2 feet long and 3 or 4 inches thick, are nearly 

 all arranged almost perfectly parallel to the primary foliation of the granite. 

 Most of the lenses are less than a foot long and an inch thick. They rarely, 

 if ever, constitute more than 10 or 15 per cent of the volume of the rock. 

 Local zones parallel to the foliation of the granite are entirely devoid of the 

 lenses, while still other zones contain relatively few of them. Individual zones 

 or helts some rods in width are remarkably uniform as regards numbers, 

 arrangement, and composition of the inclusions, certain definite zones of this 

 kind having been traced almost without interruption along the barren ledges 

 for one-fourth of a mile or more. Not only is the foliation of the lenses and 

 of the granite (and zones of granite) parallel, but also these are parallel to 

 the long axes of the two areas of lens-bearing granite. 



Figure 1. — Sillimanite-sehist Inclusions in Granite near South Russell, New York 



Examination of a number of thin sections of the lens material shows it to 

 be very uniform in composition, or about as follows by volume percentages : 

 quartz, 60 to 75 ; sillimanite, 25 to 40 ; magnetite, one-fourth to 4 ; muscovite, 

 one-fourth ; and in some cases very little zircon or pyrite. The quartz is 

 granular, while the sillimanite nearly all occurs in the form of needles, many 

 of them singly and many of them in bundles. Many of the bundles consist of 

 crudely parallel needles, while others form more or less curving to plumose 

 bundles. Most of the sillimanite needles lie between the quartz grains parallel 

 to the foliation, but a good many occur as inclusions in the quartz. Some of 

 the sillimanite is in the form of broad, euhedral prisms up to one-half of an 

 inch long. 



The material of the lenses is highly foliated or schistose, this structure 

 being notably more highly developed than it is in the adjacent (or inclosing) 

 granite. The lenses are fine-grained to moderately medium-grained, except 

 for the needles of sillimanite which range in length up to one-half of an inch. 

 The magnetite occurs as tiny scattering grains, and the muscovite as tiny 

 flakes. 



