Vol. 4 1 Knopf-Thelen. — Geology of Mineral King. 249 



The clay slates in general possess the plane-parallel cleavage, 

 but, nevertheless, frequently grade into finely foliated schists. 

 Transitions between clay slates, phyllites, and microcrystalline 

 biotite schists are of constant occurrence. In the strongly schis- 

 tose varieties the biotite becomes macroscopically visible in the 

 form of minute scales. The microscope shows that the clay slates 

 contain a large amount of flaky chlorite, which becomes replaced 

 by biotite with advancing schistosity. Intercalated with the 

 clay slates and phyllites are beds of slates showing curious ellip- 

 tical depressions and pustular swellings about a tenth of an inch 

 in diameter upon the cleavage sui'faces. This peculiar phenom- 

 enon was developed in extraordinary degrees in beds occurring 

 between a succession of normal clay slates exposed in a creek- 

 cutting northeast of Mineral King. The exposure was at the 

 maximum distance possible from the granite. A thin section 

 cut from this rock when held to the light shows a remarkable 

 satiny shimmer, and reveals a large number of variously oriented 

 eye-like areas surrounded by carbonaceous bands. Under the, 

 lens the rock is found to be exceedingly fine grained and dimly 

 polarizing. Some quartz, and an abundance of green chlorite 

 is recognizable with certainty. The chlorite is very feebly bire- 

 fringent and shows a faintly luminous ultra-blue. Large areas 

 are completely isotropic owing to the overlapping of chlorite 

 scales. Some thonschiefernadeln and a few minute prisms of 

 tourmaline were noted. Carbonaceous matter is quite abundant. 

 The elliptical areas previously mentioned are sometimes bounded 

 by bands of chlorite, but are more usually defined by carbona- 

 ceous material. They do not differ essentially in composition 

 from the ground, but in a few cases were found to contain a 

 more brightly polarizing mineral. It gave straight extinction, 

 and appeared to be white mica, but its identity could not be 

 conclusively established. 



An interesting quartzite occurs near the Empire mine (alti- 

 tude 10,000 feet and N.E. of Mineral King). It is massive and 

 non-schistose, and shows three splendid jointages which cause 

 it to break in small polygonal blocks. Particles of a yellowish 

 green mineral are uniformly scattered through it, and lend it a 



