218 WATSON AND CLlNE ROCKS OF THE BLUE RIDGE REGION 



In conclusion, it may be stated that while certain striking differences 

 are apparent in the type from the Adirondacks and the Blue Eidge, yet 

 there are equally as strong resemblances, and the Blue Eidge rocks dis- 

 cussed in this paper seem to be more closely similar to those of the 

 Adirondacks than of any similar large area in this country. 



COMPARISON WITH OHARNOCKITE *> 



The charnockite series of southern India includes a group of Archean 

 hypersthene rocks which range in composition from granite to pyroxenite, 

 the members being so related as to constitute a distinct petrographic 

 province. The more siliceous varieties, though rare, are pyroxene diorites 

 and hypersthene granites (77.47 per cent Si0 2 ), and the more mafic ones 

 are norites (50.04 per cent Si0 2 ) and pyroxenites (46.86 per cent Si0 2 ). 

 However, the most abundant representative of the series is a rock of inter- 

 mediate composition containing about 63.77 per cent Si0 2 . It is char- 

 acterized by abundant andesine with orthoclase, often perthitically inter- 

 grown, with hypersthene, and blue and gray quartz. Augite, hornblende, 

 and biotite occur, the first two being remarkably uniform in character in 

 all occurrences of the charnockite series and are almost as characteristic 

 as hypersthene. 



Analyses of Rocks of the Charnockite Series s0 



(H. S. Washington, analyst) 



I 



Si0 2 77.47 



ALO, 11.00 



Fe 2 O s 1.04 



FeO 2.02 



MgO . .. 0.43 



CaO 1.02 



Na 2 2.86 



K 2 4.14 



H 2 0+ 0.20 



H 2 0— 0.05 



Ti0 2 0.26 



Zr0 2 



P 2 5 none 



S 



Cr 2 O a 



II 



63.85 

 14.87 

 2.32 

 5.07 

 3.29 

 4.48 

 3.72 

 1.09 

 0.11 



0.83 



trace 



0.08 



0.15 



none 



III 



50.04 



11.65 



2.63 



15.76 



5.58 

 7.89 

 3.08 

 0.89 

 0.19 



1.93 



0.20 



IV 



47.44 

 5.36 

 3.13 

 12.42 

 19.96 

 7.60 

 0.48 

 0.10 



0.08 



1.29 

 none 

 0.27 

 0.34 

 0.07 



28 T. H. Holland: Memoirs Geol. Survey of India, vol. xxviii, part 2, pp. 119-249; 

 Quart. Jour. Geol. Soc. London, vol. 53, 1897, p. 405. 



30 We wish to express to Dr. H. S. Washington our sincere appreciation for his kind- 

 ness in granting us permission to use the four complete analyses recently made by him 

 of rocks belonging to the charnockite series, for which grateful acknowledgment is made. 



