ON SOME GLAUCOPHANE AND ASSOCIATED SCHISTS 

 IN THE COAST RANGES OF CALIFORNIA. 1 



The blue amphibole or glaucophane schists of the California 

 Coast Ranges, with which are genetically associated actinolite 

 and garnet schists, have been objects of considerable geologic 

 interest since they were first observed in 1877. They have been 

 cited by Mr. H. W. Turner, 2 Dr. H.W. Fairbanks, 3 and by others 

 from many parts of the Coast Range mountains, throughout 

 which they are abundant. 



The schists occur to a large extent as rather massive isolated 

 outcrops, and, in general, do not show their schistose structure 

 except upon a near examination. They vary in texture from 

 layer to layer ; a hard, compact quartzose sheet being succeeded 

 by a wrinkled, elastic, micaceous layer, which may be followed by 

 a dense massive variety containing but little mica. These 

 schists are for the most part entirely crystalline, and are princi- 

 pally characterized by the abundance of blue amphibole or glau- 

 cophane, which they contain. Whether this blue amphibole is 

 mainly glaucophane, crossite or riebeckite the writers have not 

 determined. There appear to be at least two varieties of the 

 blue amphibole present in the series, one with a wide angle 

 between the optic axes and strong double refraction, and another 

 with a very narrow angle and weak double refraction. For the 

 sake of convenience, however, and in accordance with the gen- 

 eral practice, the blue amphiboles will be referred to in this 

 paper as glaucophane. 



'The writers are indebted to Dr. J. P. Smith, of Stanford University, for assist- 

 ance and advice. 



2 "Notes on Some Igneous, Metamorphic and Sedimentary Rocks of the Coast 

 Ranges of California," H. W. Turner, Jour. Geol., Vol. VI, p. 488 etseq.; "The 

 Geology of Mount Diablo, California," H. W. Turner, Bull. Geol. Soc. Am., Vol. II, 

 P- 385. 



3 "The pre-Cretaceous Age of the Metamorphic Rocks of the California Coast 

 Ranges," H. W. Fairbanks, Am. Geol., Vol. IX, p. 160 ; " Notes on a Farther Study 

 of the pre-Cretaceous Rocks of the California Coast Ranges," H. W. Fairbanks, 

 Am. Geol., Vol. XI, pp. 70-73. 



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