PROCEEDINGS 



OF THE 



AMERICAN PHILOSOPHICAL SOCIETY 



HELD AT PHILADELPHIA 

 FOR PROMOTING USEFUL KNOWLEDGE 



Vol. XLV October-December, 1906. No. 184. 



THE PARAGENESIS OF THE MINERALS IN THE GLAU- 

 COPHANE-BEARING ROCKS OF CALIFORNIA. 



By JAMES PERRIN SMITH, 

 Stanford University, California. 



Communicated by Prof. J. C. Branner. 



{Read October 5, 1906.) 



Occurrence of Glaucophane-bearing Rocks in California. 



Glaucophane-bearing rocks are widely distributed in the Coast 

 Ranges of California, in the Franciscan series, commonly associated 

 with serpentine (altered peridotite). The rocks that contain glau- 

 cophane are classed together because of the occurrence of this min- 

 eral, but they are of widely different characters and origin. It 

 is likely, however, that they were all affected by the same sort of 

 metamorphism, although the writers that have discussed these rocks 

 are by no means agreed as to whether this metamorphism was due 

 to contact or to dynamic action. 



No glaucophane is developed in the extensive series of mica 

 schists along the granite contacts of the Coast Ranges, where mi- 

 caceous and hornblendic gneissic and schistose rocks are abundant. 

 And yet those schists are not essentially different in chemical nature 

 from the glaucophane rocks. In the Franciscan series, on the other 

 hand, glaucophane is abundant in altered rocks ranging in character 



PROC. AMER. PHIL. SOC, XLV. 183L, PRINTED JANIZARY 9, I907. 



