534 DESCRIPTIVE GEOLOGY. 



white flakes of mica, which are, in general, disposed parallel to the bedding 

 of the quartzite, and, as a microscopical constituent, fine black threads of 

 hornblende and minute dislocated prisms of actinolite. The quartzites 

 of Clover Canon represent the lowest part of the quartzitic series, and pos- 

 sibly a lower series than those exposed on the west side of the mountain, 

 west of Clover Peak. They are distinctly fissile, and split with ver}^ 

 smooth faces, upon which are clearly seen striations not unlike the 

 slickensides frequently observed in mines. The surfaces of these laminae 

 are more or less discolored and spangled with plates of pure white mica. 

 Occasionally rare small crystals of feldspar appear on these smooth 

 brownish faces. The appearance of striation is in no way referable to the 

 presence of mica, but is an actual rubbing and grooving of the surface 

 face from some early motion. In the quartzites of the entire group, this 

 phenomenon is not uncommon, nor is it confined to the quartzites ; but the 

 mica-schists themselves show evidence of internal motion. 



Along the west side of the range, in the vicinity of Thompson's Ranch, 

 the quartzites are less milky and of a clearer gray tint ; and although they 

 still carry white mica, they have some black biotite. The same cleavage- 

 faces are developed, but here they are decidedly corrugated and ribbed by 

 mica, which enters the face at a diagonal ; the whole appearance is as if 

 the cleavage-face had been developed obliquely to a zone of parallel mica 

 flakes. Besides the white mica in these last quartzites, there is a considera- 

 ble amount of finely fibrous green mineral, which, in localities, is more or 

 less penetrated by half-decomposed and almost wholly-decomposed white 

 mica. This green mineral is doubtless a chloritic decomposition-product 

 of the mica. Such behavior of the mica in these quartzites is of interest 

 as illustrating the transition from well-defined crystalline schists with a par- 

 allel structure to granitoid forms, in which such structure is no longer 

 observable. The lack of parallelism in the mica flakes, and the lack of 

 continuity of the planes which carry mica, already suggest the granitoid 

 structure. As in the Clover Canon quartzites, so here also is there an appear- 

 ance of severe horizontal rubbing. The chloritic mineral, the mica, and the 

 quartz, all show evidences of powerful attrition and pressure. 



No garnets are observed in the quartzites of the west side. Under the 



