154 



QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



groups. A few small grains, but no lath-like microlites, of plagioclase and 

 a group of augite and liyperstliene crystals also appear. Tlie niicroscope 

 thus confirms the reference of this material to the andesitic eruptions. This 

 specimen was analyzed with the result given below. 



For comparison with this glass an analysis was also made of No. 7, 

 Clear Lake, an asperite from the southeast peak of Mt. Konocti. This rock 

 contains a few quartz grains, but is otherwise similar to most of the asperites 

 of the region. It is sensibly holocrystalline. The components are plagio- 

 clase, augite, hypersthene, iron ores, and quartz. The porphyritic feld- 

 spars are probably andesine. The hypersthene occurs in prisms of consid- 

 erable length, while the augite is found in small grains. The groundmass 

 is chiefly made up of microlites and irregular grains of plagioclase. The 

 rock is slightly decomposed and contains a little calcite. 



In the following table, I is the andesitic obsidian. No. 13, Clear Lake, 

 and II is the asperite, No. 7, Clear Lake, just described: 



Atomic ratio of I, H= : .Si : R>i : R"=0.032 : 4.934 : 0.760 : 0.363. 

 Atomic ratio of II, II- : .Si+Ti : ^l" : R"=0.03-2 : 4.403 : 1.0:)4 : 0.418. 



The obsidian is much more acid than the holocrystalline rock into 

 which it passes by transitions, but this is not the only chemical difference. 

 The sum of the quantities of lime iind magnesia is less than one-third as 

 great as the corresponding sum in tlie asperite, while the glass contains 



