274 



PENTTI ESKOLA 



amount increases with the quantity of the femic compounds, a fact 

 indicating that it is a substitute for anorthite. The epidote occurs 

 as clear, individual crystals, often intergrown with quartz in the 

 myrmekite fashion. 



Another feature significant in connection with the conditions 

 of formation of these banded gneisses is the absence of perthitic 

 threads of plagioclase in the microcline, which is clear and finely 

 cross-hatched. The texture, on the whole, is aplitic, and all the 

 main minerals are equally xenomorphic. 



Fig. 3. — Banded clinopyroxene gneiss. W. of Benson Pond, Washington, 

 Massachusetts. Eight-ninths natural size. 



Emerson {op. cit., p. 153) published an analysis of clinopyroxene 

 gneiss, called by him " titanite-pyroxene diorite aplite," from 

 "east of C. Conwell's place. South Peru, Mass." The analysis, 

 made by W. T. Schaller, is quoted below (p. 275). 



I have found these clinopyroxene-bearing rocks to be exceedingly 

 variable in composition, and the analysis has happened to be made 

 on a rather exceptional type. Most specimens collected by us 

 from the same tract and, also, one collected by Professor Emerson 

 from the Peru line, "the same ledge as the rock analyzed" {U.S. 



