B. 8. Butler — JPyrogenetic Epidote. 27 



Art. Y. — Pyrogenetic Epidote ;* by B. S. Butler. 



Ax occurrence of epidote as an apparently original constitu- 

 ent of a dike rock was observed by the writer in 1907, while 

 engaged in field work in the Shasta County copper region, 

 California. This recalled the question as to whether or not 

 epidote is ever a pyrogenetic mineral. In the occurrence to 

 be described, the evidence of primary origin seems unusually 

 good, and, although the material obtained is not as fresh as 

 could be desired, since all the specimens were collected from 

 surface outcrops, yet it is thought worthy of presentation. 



In order that the evidence may be properly weighed, it may 

 be well to preface it with a brief review of some of the occur- 

 rences described by previous observers. 



One of the best known of these in the United States is that 

 of allanite and epidote in the granites of Uchester, Maryland, 

 described by Professor W. H. Hobbs.f Concerning the origin 

 of the minerals Professor Hobbs says: "With little doubt the 

 latter (allanite) is one of the earliest separations from the 

 magma. The origin of the epidote is not so easily settled, but 

 the i stretched ' character of the granite is in favor of a meta- 

 morphic origin, through pressure. Against such a view is the 

 discovery by Professor Williams that the Woodstock granite, 

 which is particularly rich in these intergrowths, shows no evi- 

 dence of cataclastic action.' 1 ;}; In a later publication the author 

 expresses the belief that the epidote of the Uchester granites, 

 in some cases at least, is an original mineral. The Maryland 

 granites were later studied by Mr. C. R. Keyes,§ who concludes 

 that both the allanite and epidote are of primary origin. A. 

 Lacroixf describes intergrowths of epidote and allanite closely 

 resembling those of Uchester, in which the epidote is con- 

 sidered as an original mineral. Professor W. C. Brogger^f 

 describes similar intergrowths and considers the epidote, in 

 some cases at least, to be of pseudomorphic origin. Professor 

 Frank D. Adams*"* describes the occurrence of epidote and 

 allanite in granites from Wrangell Island, Alaska, and Pelly 

 River, Yukon district, Alaska. In both cases the epidote is 

 considered as a mineral which has grown in the rock after its 

 consolidation, but without recrystallization of the other con- 

 stituents. 



* Published bv permission of the Director of the U. S. Geological Survey. 



f This Journal (3), vol. xxxviii, pp. 223-228. 



\ Am. Geol., vol. xii. p. 218, 1893. 



gGeol. Soc. Am. Bull., vol. iv. pp. 305-312. 



I Bull, de la Soc. Francaise de Mineralogie, vol. xii, Apr. 1889. 



1[ Zeitschrif t fur Krystallographie, xvi, p. 99, 1890. 



** Canadian Eecord of Science, 1891, p. 344. 



