NO. 1715. OLIVTNE-DIABA8E FROM NORTH CAROLINA.— POGUE. 



481 



Classification in the quantitative system."- — From the chemical analy- 

 sis of the rock previously given, its position in the quantitative system 

 may be determined by calculation of the norm, as follows : 



Calculation of the norm of kcdabekase (olivine-diabase) . 



Or .*. 1.671 



Ab 9.43i57.53 



An 46.43J 



Di 2.261 



H.y 28.30[4j_gg 



01 



Mg. 

 H2O 



Class, 

 Order, 

 Rang, 



Sal 57. 53 . 

 Fein" 41. 89 



F 57.53 

 KzO + NajO 



CaO 

 Subrang, not needed 



= 1.3=111, salfemane. 

 =0=perfelic=5, gallare. 



= .12=percalcic=5, kedabekase. 



Weathering. — The olivine-diabase is not very susceptible to super- 

 ficial alteration. Where cut by joint planes, however, it forms con- 

 centrically weathered bowlders with a yellow or rust-colored exterior. 

 This coating of clay-like material stained with iron oxide is only a 

 very small fraction of an inch in thickness, and beneath is revealed the 

 fresh rock. The soil resulting from the complete decomposition of 

 these bowlders is a rust-colored clay with very little grit. 



LITERATURE ON OLIVINE-DIABASE OCCURRING IN THE UNITED 



STATES. & 



1. Campbell, H. D., and Brown, W. G. Composition of certain igneous rocks of 



Virginia. 



Bull. Geol. Soc. Am., vol. 2, 1891, pp. 339-S47. 



Gives the chemical composition of an olivine-hypersthene diabase from Culpeper County, Vir- 

 ginia. 



a As proposed by Cross, Iddings, Pirsson, and Washington in 1903. For explana- 

 tion of this method of classification the reader is referred to their book, The Quanti- 

 tative Classification of Igneous Rocks. 



^This bibliography is not intended to be exhaustive. It contains, however, the 

 most important articles, in which are included petrographic or chemical descriptions 

 of olivine-diabase. There are references to no less than several hundred articles on 

 "trap rock" in the so-called Newark series alone (see I. C. Russell, The Newark 

 System, Bull. No. 85, U. S. Geol. Survey, 1892), and many of these are what would 

 now be termed olivine-diabases. 



Proc.N.M.vol. 37—99 31 



