136 



University of California. 



I Vol. 3. 



In a slide from a second specimen, there occurs an additional 

 phenomenon of peculiar interest. Although the body of the 

 quartz grains here is free from any inclusions within the range 

 of the highest powers available to the writer, each grain contains, 

 a little within the periphery and parallel to it, a zone of minute, 

 apparently gaseous inclusions. There can be no doubt that their 

 presence is due to the action of the heated magma during the 

 absorption of the grain. 



A chemical analysis by the writer is given below, with one of 

 a quartz-basalt from the Lassen Peak district described by Diller, 

 for comparison. 





I. 



II. 



SiO, 



59.61 



57.25 



A1 2 3 



15.98 



16. 45 



Fe 2 0, 



1.12 



1.67 



FeO 



5.42 



4.72 



MgO 



5.04 



6.74 



CaO 



5.54 



7.65 



Na 2 



3.68 



3.00 



K 2 



1.10 



1.57 



H 2 at 110° 



0.20 





H 2 above 110° 



1.14 



0.40 



Ti0 2 



0.65 



0.60 



P 2 5 



0.14 



0.20 



MnO 



0.21 



0. 10 



NiO 



0.05 





SrO 



trace? 



trace 



BaO 



0.04 



0.03 



Total 



99.92 



100.38 



The more important points of difference are the greater silica 

 content of the Oregon rock, the smaller percentage of lime and 

 magnesia and the higher ratio of soda to potash. Notwith- 

 standing these differences, there is a notable resemblance between 

 the two analyses. 



Andesite from Volcanic Neck at Cherry Creek. In the hand- 

 specimen this rock has a somewhat basaltic aspect, being 

 compact, fine-grained and of a dark iron-gray color. The speci- 

 men contains a mass, as large as an almond kernel, of milky 

 quartz somewhat discolored by iron oxide. 



I. Quartz-basalt, Cherry Creek. Analyst, F. C. Calkins. 



II. Quartz-basalt, Cinder Cone, 10 miles N.E. of Lassen Peak. Described by 

 Diller. Bull. U. S. G. S. Nos. 79 and 150. Analyst, W. F. Hillebrand. 



