Vol. 4] Knopf-Thelen. — Geology of Mineral King. 261 



chiastolite schists, over a distance of 6,500 feet along the strike. 

 At Cisco on the Colfax Quadrangle Lindgren has mapped in 

 several square miles of hornfels rocks, and has shown the exist- 

 ence of a hroad contact zone half a mile wide and several miles 

 long. The conditions there parallel closely those obtaining at 

 Mineral King. The plane of intrusive contact is nearly ver- 

 tical, and is in its general trend closely coincident with the strike 

 of the invaded formations. 



The belt of rocks with which we are concerned narrows down 

 south of Farewell Gap to as small a thickness as 4,200 feet across 

 the strike. The major portion of the series consists of normal 

 •clay slates, and comprises the axis along which the valley of the 

 Little Kern has been eroded. Two conditions were unfavorable 

 to the metamorphic activity of the granite ; firstly, the vertically 

 of the contact walls, and secondly, the parallelism of the strike 

 of the strata with the contact plane. Opposed to these unfavor- 

 able conditions were the great narrowness of the belt, and the 

 simultaneous supply of heat from two opposite sides. The de- 

 gree of metamorphism, therefore, appears relatively small, and 

 Is but insignificant when compared with what has been effected 

 in other portions of the Sierra Nevada under less favorable con- 

 ditions. The frequent occurrence of tourmaline in the invaded 

 formations, both sedimentary and volcanic, seems to show that 

 pneumatolytic processes, at least, have been comparatively ac- 

 tive. 



The description of the intrusive nature of the contact shows 

 that the trough in which the sedimentary rocks lie embedded 

 ■cannot have originated through faulting, either of simple or 

 graben character. The irruptive character of the granites has 

 been sufficiently emphasized and the detailed evidence presented 

 as to the sunken condition of the stratified belt of rocks. It is, 

 therefore, evident that the Mineral King lens represented a por- 

 tion of the batholithic roof which has foundered during the intru- 

 sive ascent of the igneous magma. The granites were still in a 

 highly mobile condition when this event took place, but evidence 

 deduced from the incommensurate degree of thermal meta- 

 morphism seems to indicate that the submergence did not long 

 .anteeede the final consolidation of the magma. 



