478 THE CRYSTAL FALLS lEON-BEARING DISTRICT. 



character, large and small spicules and plates of sericite, crystals of magne- 

 tite, and a few needles of chlorite and other secondary substances. Between 

 these, again, is often a cement of what seems to be secondary quartz. The 

 schistosity of the specimens is due to the arrangement of the sericite in 

 approximately parallel positions, and to the elongation of the quartz grains 

 in the same direction. The pink color of the rocks is produced by red 

 earthy substances in the feldspars and in their decomposition products. 



In the most schistose phases of the conglomerates the quartz pebbles 

 have been mashed into plates, several of which join, end to end, forming 

 sheets, which in the thin section appear as long narrow lines of variously 

 oriented quartz grains, each of which is crossed by strain shadows. 



The larger quartz grains in their matrices are broken into parts, and 

 these parts are differently oriented with respect to one another. Other 

 grains seem to have entirely recrystallized, for they are now made up exclu- 

 sively of the same kind of intei'locking quartzes as are present in the fine 

 portions of the groundmass in which the coarse quartz grains are embedded. 

 In the groundmass of these rocks sericite is very abundant, and feldspar is 

 rare. From the proportions of these minerals present it would appear that the 

 former has been derived larg-ely from the latter. Biotite is also present in 

 many specimens as small green flakes, but this mineral is not widely spread. 



The conclusion from the study of the thin sections of the schistose 

 conglomerates is that there has been a crystallization of new substances, 

 principally quartz, sericite, biotite, and magnetite, from the materials of the 

 original granitic sediments. Perhaps a portion of the crystallization was 

 the result of alteration of the original components before squeezing took 

 place. The larger portion, however, was accomplished under the influence 

 of pressure. The result of the mashing and recrystallization is a schist, 

 which between crossed nicols has the aspect of a typical crystalline schist, 

 but which in natural light exhibits its conglomeratic nature in the presence 

 of the large quartz lenses, with the outlines of flattened pebbles, in a fine- 

 grained groundmass. 



The pink arkoses differ from the conglomerates simply in the absence 

 from them of the pebbles. The schistose varieties are similar in every 

 respect to the schistose groundmass of the squeezed conglomerates. Both 

 in the hand specimen and in the thin section the schistose arkoses exhibit 

 striking resemblances to muscovitic gneisses. 



