PETIIOGRAPHICAL CHAEACTEK OF MESXAKD QUAKTZITE. 229 



In the matrix serieite lias almudantly (k'veloped, and tlie leaflets are 

 parallel. The mhnite spaces formed by the shattering- of the larg-e frag- 

 mental grains and those in the background are filled with secondary cherty 

 quartz, whicli has thoroughly cemented tlie rock. The larger fractures are 

 filled with cherty quartz, forming veins. In many of these are fragmeutal 

 grains broken off" from the main mass of slate. 



In the phase in which the dynamic action was still more severe the gray- 

 "wackes were shattered through and through, the particles having moved and 

 ground over one another. As a result of this there were left innumerable 

 minute spaces, which have been taken advantage of by the infiltrating sil- 

 ica, and are now filled with secondary cherty quartz. The original frag- 

 meutal quartz grains are always somewhat granulated on their exteriors, 

 and many throughout, so that a quartz grain is represented by a lenticular 

 mass of finely interlocking quartz. In the matrix the sericite has developed 

 in coarser blades than in the less metamorphosed rocks. It is everywhere 

 in long, narrow leaflets having a parallel arrangement in the same direction 

 as the elongated quartz grains. Numerous veins are completely filled with 

 interlocking, coarsely and finely crystalline quartz, apparently all of it being 

 secondary. If any of the original fragmental quartz grains have dropped 

 in the crevices, they have become so shattered as to have lost their rounded 

 outlines. 



The conglomerates, quartzites, and graywackes of the IMesnard for- 

 mation include rocks varying from those which are indtu-ated mainly by 

 siliceous cementation to those which are crystalline schists. From their 

 macroscopical and microscopical descriptions it is plain that there has every- 

 where been interior movement. Even in the least altered phases of the 

 rock every grain of quartz shows the eff"ect of strain. From this least altered 

 phase there are all gradations to those phases in which the rock is a 

 shattered or mashed mass cemented by cherty quartz. Moreover, after 

 a first shattering and cementation there was a later folding, wdiich again 

 shattered the rock, including both the original constituents and the sec- 

 ondary cherty quartz. This broken rock was again cemented by later 

 infiltrating silica. 



In certain parts of the formation, where the relief was largely by 



