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



237 



granite from three to four feet wide, is an enormous assemblage 

 of dark-colored ellipsoidal enclosures, so numerous as to con- 

 stitute more than one-half the bulk of the rock. The contact is 

 exposed to a vertical height of 20 feet at points, and horizontally, 

 several hundred feet, and the inclusions are seen to have sub- 

 ordinated the granite to the function of a mere binding material. 

 They have been oriented parallel to the plane of the contact, and 

 show distinct evidences of plastic deformation, being somewhat 

 flattened in the direction of their major axes. Texturally they 

 are fine grained aggregates of the dark and light constituents. 

 In thin section it is seen that the ferromagnesian minerals, rep- 

 resented by biotite, hornblende and augite, comprise half or 

 more of the bulk of the slide. The biotite exceeds slightly the 

 hornblende plus the augite. The hornblende, which is of the 

 common green variety and strongly pleochroic, is frequently 

 irregularly intergrown with pale green augite with the c axes 

 common. The feldspars present are orthoclase and calcic oligo- 

 clase, associated together in nearly equal proportions. Quartz 

 is very subordinate; a small but variable amount of micro- 

 graphic (myrmectic) intergrowth is recognizable. The most 

 noteworthy feature, however, is an extraordinary abundance of 

 perfect apatite needles, often of long slender, acicular habit, 

 with a length exceeding fifty times the breadth. Such needles 

 must furnish sensitive indicators of any internal movements 

 since the consolidation of the magma. The apatite is perhaps 

 four or five times as plentiful as in its granite host. Zircon, 

 titanite, pyrite and magnetite are sparingly represented. The 

 structure is allotriomorphic granular, though occasionally the 

 biotite shows sharp idiomorphism. 



The host is a fairly coarse grained quartzose granite carry- 

 ing a great deal of biotite and considerable hornblende. The 

 foliae of biotite show an incipient effort to congregate, and give 

 the granite a faint appearance of inhomogeneity. The micro- 

 scope shows that orthoclase is the dominant feldspar, and that 

 but a very small amount of acid plagioclase is associated with it- 

 Apatite (somewhat more abundant than in normal granites), 

 zircon, magnetite, and titanite comprise the accessories. 



