508 H. IV. TURNER 



the Greek word irep/cvo^, meaning dark. It will include graiio- 

 lites of the following specific names : 



Pj^roxenite. 



Hornblendite (Williams). 



Websterite (Diallage and ortho-rhombic pyroxene) (Wil- 

 liams). 



Diallagite. 



Hornblende-hypersthene rock (Merrill). 



Amphibole-pyroxene rock (Turner). 



The group may be graphically represented by the method 

 employed by Hobbs^ and his representation of a composite 

 pyroxenite will approximate to that of a typical perknite. The 

 following table of analyses will give the reader a notion of the 

 composition of the rocks which may be properly included in 

 this group. 



1. Horjibleiidite. — Geo. Steiger, analyst. This partial analy- 

 sis is here published for the first time. The rock is from a dike 

 cutting through the basement complex and overlying Cambrian 

 rocks, 2 km north of Silver Peak village, in Esmeralda county, 

 Nev. It is composed chiefly of green hornblende with some 

 feldspar. The rock grades into a basic diorite. 



2. Ajnphibole-pyroxene rock. — W. F. Hillebrand, analyst. Not 

 before published. Rocks of this type are very abundant in 

 Mariposa county, Cal. Mr. F, M. Anderson, of the University 

 of California, has likewise collected them in northern California. 

 This rock in its typical development is composed of original 

 pyroxene and amphibole in grains of nearly equal size, with a lit- 

 tle quartz and pyrrhotite. Scattered through the rock are pheno- 

 crysts about one centimeter in diameter, of brown amphibole, 

 which contain in a poikilitic manner, as inclusions, the constitu- 

 ents of the groundmass. 



3. Perk7iite {^a.\x{hor's ndiVsxe, peridotite^. — Belchertown. Bull. 

 U. S. Geol. Survey, No. 168, p. 30. L. G. Eakins, analyst. The 

 rock is composed of hornblende, pyroxene, biotite, olivine and 

 magnetite. 



'Jour. Geol., Vol. VIII, 1900, p. 14. 



