REPORT OF THE DIRECTOR I917 IO3 



From a study of the thin sections of the rocks of these two masses 

 and from the results obtained by grouping them according to their 

 degree of crushing, the following conclusions have been drawn, 

 based on the accompanying briefly summarized data : 



1 There are three well-defined bands or zones of metamorphism 

 in which increasing degrees of crushing are exhibited passing from 

 the southeast to the northwest ; comprising (a) gneiss of the southeast 

 zone in which there is no evidence of crushing and in which the 

 texture is of massive granitoid character (plates i and 4) ; (b) proto- 

 clastic gneiss of the central zone in which most of the minerals 

 are granulated but in which quartz is uncrushed (plate 2) and (c) 

 cataclastic-protoclastic gneiss of the northwest zone in which most 

 of the minerals are pulverized but in which quartz is only granulated 

 (plate 3). The line between (b) and (c) has been drawn where the 

 quartz first starts to appear granulated and where the average 

 diameter of the pulverized feldspar grains averages less than 0.1 mm 

 in diameter. 



2 The uncrushed gneiss is equigranular, the crushed gneisses are 

 porphyritic in texture (plates 1, 2 and 3). The gneiss which in 

 thin section shows no evidence of crushing forms, so far as mapped, 

 a band with a minimum width of 10 miles covering the eastern 

 portion of the Lowville area and the southeast corner of the Lake 

 Bonaparte quadrangle. It embraces all the gneisses belonging to 

 the Croghan syenite-granite complex. The crushed gneisses form 

 a band 5 miles wide, so far as mapped, and comprise the gneisses of 

 the Diana syenite complex. 



3 Foliation and banding are always parallel. No matter in what 

 direction the belts extend nor how abrupt the curve at the blunt 

 end of a lense, the foliation always remains parallel to the banding. 



4 The degree of crushing is for the most part independent of the 

 chemical or mineralogical composition. Rocks varying all the way 

 from hyperite to granite occur in each zone of metamorphism and all 

 within a given zone are equally crushed or equally uncrushed as the 

 case may be. 



5 The foliation is for the most part independent of the degree of 

 granulation or crushing (plates 1, 2 and 3). The gneisses of massive 

 texture exhibit as well-defined a foliation as do the pulverized cata- 

 clastic gneisses. The line of equal crushing or demarkation between 

 the protoclastic and cataclastic-protoclastic gneiss cuts directly 

 across the banding and direction of foliation of the gneisses northwest 

 of Croghan. The foliation of the gneisses in this area (the northwest 



