B. S. Butler — Pyrogenetio Epidote. 



29 



among the pyrogenetic minerals, and Mr. William H. Emmons,* 

 in a later article: u A genetic classification of minerals," ques- 

 tions its occurrence as an original constituent of igneous rocks. 



The epidote in Shasta County, California, occurs as an 

 accessory mineral in small dikes cutting an extensive mass of 

 soda-granite porphyry. This main intrusive is the enclosing 

 rock of the copper deposits west of the Sacramento River. It 

 is roughly elliptical in outline with major diameter exceeding 

 10 miles and the minor diameter 3 to 4 miles. Near the cen- 

 ter of this intrusive mass, in the vicinity of the Balaklava, 

 Shasta King, and Spread Eagle mines, are several small dikes 

 which appear, from field relation and chemical composition, to 

 be the result of differentiation from the main intrusive rock." 

 It is in these dikes that epidote is found with the characteris- 

 tics of an original mineral. 



Both the large intrusive mass and the dikes are of unusual 

 composition, being characterized by very low content of potas- 

 sium and calcium with high soda. 



Analyses of the soda-granite porphyry and one of the dikes 

 by Mr. George Stieger, of the IT. S. Geological Survey, give 

 the following composition : 



I II 



SiO 



80*09 



68-75 



Al 2 O s 



10-80 



16-75 



Fe 3 3 



FeO 



McO 



CaO 



NaO 



1-07 



-83 



-58 



-38 



.... 5-60 



•48 



1-72 



•83 



•89 



6'95 



KO 



none 



•80 



H 2 0- _ 



-24 



•84 



H 2 + 



-52 



1-52 



TiO, 



Zr0 9 



-16 



-01 



•27 

 none 



co, 



PO 



none 



-04 



none 

 •16 



so 3 



S 



MnO _ 



BaO 



SrO 



none 



none 



-02 



none 



none 



none 



none 



•04 



•03 

 •03 









100-34 10006 



I. Soda-granite porphyry near Shasta King mine. 

 II. Porphyry dike near mouth of north tunnel of Spread Eagle 

 mine. 



*Ecou. Geol., vol. iii, p. 611, 1908. 



