88 QUICKSILVEE DEPOSITS OF THE PACIFIC SLOPE. 



grains of granitic quartz and feldspars, but it also becomes apparent that 

 a great proportion of the allothigenetic minerals have been converted 

 into aggregates of new minerals. Especially important is tlie presence in 

 this slide of uncpiestionably autliigenetic augite and hornblende. Augite 

 occurs in several places under circumstances which place its autliigenetic 

 character beyond doubt. Of these the best is illustrated in the accompa- 

 nying Fig. 2. It is a slightly greenish prism with terminal faces forming 

 angles on the right and left sides, respectively, of 12.5° and 128°, and an 

 angle of extinction of about 30°. It occurs in a crystalline aggregate fill- 

 ing the position of a clastic grain of which the outlines are traceable. Tlie 

 portion not occupied by the augite is composed of microcrystalline feld- 

 spar and quai-tz. There are also films of serperitine among the grains. 

 The upper right-hand corner of the augite is changed to uralite. 



Flo. 2. Aiitbigenetic aiigitp ■ 



altoreil sanilatnne, No. 8, Coast Ranges. A. an<rite; 11, nralitei /, niicrocrystallii 

 11 ; ./, ciuaitz graiu ; s, aerpentino. Magnified 117 diameters. 



Autliigenetic hornblende of light-brown color is also present, and the 

 best example appears in the following Fig. 3. It is surrounded on two 

 sides by microcrystalline, authigenetic feldspar and lies against a clastic 

 orthoclase grain. As appears from the cut, a large part of the outline is as 

 sharp as possible. The unabraded corners, the color and character of the 

 mineral, and the association all forbid its being regarded as allothigenetic. 

 On the left side are a number of hornblende microlites in parallel position, 

 apparently representing the incomplete portion of the crystal. 



