lawsok.] Plumasite, an Oligoclase- Corundum Rock. 



2121 



where corundum is found as an original constituent of certain 

 lamprophyre dykes in Yogo Gulch described by Pirsson,* who 

 refers its origin to endomorphism of the magma by absorption of 

 the adjacent shales. A corundiferous mica-augite-andesite at 

 Ruby Bar, Montana, is described by Kuntz,f and Pratt has 

 noted a corundiferous augite-miea-syenite from the same or a 

 neighboring' locality, as well as a corundiferous biotite- syenite 

 from Gallatin county, Montana. I The important occurrences of 

 corundum associated with peridotites in the Appalachian belt 

 described by Pratt appear to be concentration products on the 

 contacts of the peridotite, and may therefore be secondary rather 

 than pyrogenie, although Pratt regards them as differentiation 

 products of the same magma which gave rise to the peridotite. 



In addition to these occurrences it has been long' known that 

 •corundum exists as an accessory in a variety of volcanic rocks, 

 notably in the volcanic districts of the Rhine, but these have 

 usually been looked upon as inclusions picked up by the magma 

 and foreign to it. It seems probable, in view of the establish- 

 ment of the pyrogenie origin of corundum in the cases above 

 referred to, that many of these supposed exotic occurrences of 

 that mineral will be recognized as products of the crystallization 

 of magmas. 



The Discovery. — It is the purpose of the present paper to 

 offer a contribution to this growing body of information regard- 

 ing corundiferous igneous rocks. The writer first became aware 

 of the existence of the rock which forms the subject of the paper 

 by seeing a fragment of it in the lapidary shop of Mr. Kinrade 

 of San Francisco. He secured the specimen, and on inquiry 

 ascertained that it had been brought there by Mr. J. A. Edman 

 of the Diadem Mine, Plumas Co., Cal. He thereupon communi- 

 cated with Mr. Edman and subsequently visited him, and was by 

 him conducted to the locality where the rock outcrops. The 

 credit of the discovery of this new and interesting rock, there- 

 fore, belongs to Mr. Edman, although it is the writer's privilege 



*U.S.G.S. 20th An. Rpt., Pt. Ill, p. 554 et seq. 

 t Am. Jour. Sci., 4th Ser., Vol. IV, 1897, p. 418. 

 tOp. cit., pp. 30, 31. 



