e 



PLATE 1. 



Fiot B( I. — Mi J" tht o ght. 



\ large fragmental particle of feldspar has been to a considerable extent alt<-n-.l t" blot 1 1 



Itange has « holly destroyed the exterior of the grain, but t lie Interior appears in the 



i unit, i igainat the feldspar grain upon one shle is a large particle "f quarts. 



background Is finely crystalline quart/, an'l biotite, in which are contained a few larger parti- 



■ 



I-1..I BJ I I I :■ 1. /" tin y>n i tht. 



Theeztentol the decomposition of the feldspar to quartz ami mica la now appreciated, these 



minerals and the residual feldspar making nn intricate crystalline complex. The apparently 



simple elongated quartz-grain "f the previous figure is found to have been broken Into aeveial 



ri.\ i i 



l''l..i ia: 1. — M In tin <■ lilt. 



id consists of mica and quartz, much of the former being muscovite. The 



■ • \ double arrangement of these two micas Is very distinctly shown, 

 direction of the muscovite being nearly perpendicular i" thai of the biotite. It it 



■ the biotite particles are unusually wide, transi erae to the cleavage. Thi* double 



■ i the mica corresponds to the two direct i<>n< "i la mi nation of the rock as Been in 



I In- larger Bakes "f mica ai e regarded as having begun t" develop al the time "i 



when a new force nearly at right angles to the old one sat in, 



numerous other Individuals of mica began to form with their l< rpendicular to the 



ndividuals continued, however, to grow. 



I'h.i i:i •_'. — .1/ ;ht. 



i i uhistsol the Black mils. I ground consists ol 



with their Ion i lirection. The mica includes both mu 



■ i which, like the quartz particles, have > very perfect linear-parallel 





