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



239 



ent in no more than normal amount. The structure is hypidio- 

 morphic granular. 



The peculiar mode of occurrence of the enclosures at Eagle 

 Lake, and their great numerical abundance, seem to give the 

 contact some significance in their genesis. At first sight, it 

 would appear probable that here they represented partially 

 digested fragments of the invaded formations, but the micro- 

 scopic diagnosis, and the absence of the pronounced endomor- 

 phism which the assimilation of such large amounts of silica 

 would necessitate, argue strongly against such an hypothesis. 

 And furthermore, the deformation of the enclosures visible ma- 

 eroscopically should show corresponding structures microscopi- 

 cally. If the inclusions are of extraneous origin, and have suf- 

 fered magmatic corrosion and plastic deformation, the individual 

 mineral components should accordingly show incipient fusion. 

 The deformation has necessarily been plastic, inasmuch as the 

 drawn-out inclusions are contained in an unsheared granite as 

 host. The thin section, however, reveals no evidence of incipient 

 fusion, and shows that the various minerals possess the sharp, 

 pyrogenic outlines characteristic of granular plutonic rocks. In 

 reviewing the petrographic details it is apparent that the inclu- 

 sions represent basic segregations from the granitic magma and 

 are characterized by high concentrations of the so-called usual 

 accessories. A close sympathy between host and segregation is 

 indicated by the dominance of a peculiar accessory : apatite, in 

 the apatite-rich granites and titanite in the titanite-rich granites. 



Later Intrusives. — Intrusive into the schists and granite on 

 Monarch Creek is a quartz-mica-diorite, which, wherever ex- 

 posed, exhibits a uniform and persistent petrographic habit. The 

 contact with the granite is marked by an irregular intrusion 

 breccia, wherein the invading magma has incorporated numerous 

 angular blocks of granite. Occasionally a light colored aureole 

 three-quarters of an inch broad has been developed around the 

 acid inclusions. Other evidence indicative of the irruptive nature 

 of the quartz-mica-diorite is furnished by the frequent appear- 

 ance at the contact of porphyritic facies resembling coarse, holo- 

 erystalline andesites. 



