Washington — Charnockite Series of Igneous Rocks. 323 



Art. XXII. — The Charnockite Series of Igneous Rocks ; by 

 Henry S. Washington. 



Introduction. 



About fifteen years ago T. H. Holland* described a series 

 of igneous rocks which are found at various localities in Ma- 

 dras and elsewhere in southern India. They are said to form 

 a well-defined comagmatic region or petrographic province of 

 Archaean age,f the members of which range from a highly 

 silicic hypers thene granite, through intermediate types, to 

 norites and pyroxenites. Holland gave the name charnockite 

 to the granite, and proposed the designation " Charnockite 

 Series" for the whole group, in order to distinguish the rocks 

 of this petrographic province for survey purposes. He urged 

 the importance of applying the terms only to the rocks of 

 India. The term " series " was thus used by him much as it 

 had been used by J. D. Dana;}; twenty years before for the 

 igneous rocks of the " Cortlandt Series." While Dana did not 

 explicitly recognize the concept of a petrographical province, 

 enunciated later by Judd, yet he seems to have had some idea 

 of the " consanguinity " of the rocks. 



Holland's descriptions are quite detailed, but the analyses 

 which he cites are not very satisfactory, chiefly because of the 

 non-separation of the iron oxides, and to a less extent because 

 none of the minor constituents was determined. The high 

 summations are most probably due to the FeO being reckoned 

 as Fe 2 3 , the extra oxygen involved increasing the apparent 

 sum. 



As the rocks are of importance in Indian geology and are of 

 considerable penological interest in that they present great 

 similarities with rock series elsewhere, a chemical reexamina- 

 tion was deemed advisable. At the request of Di\ L. L. Fer- 

 mor, the Geological Survey of India, through Mr. Guy C. 

 Pilgrim, sent me five excellent specimens of typical representa- 

 tives of the charnockite series, the specimen numbers being 

 the same as some of those described by Holland. There were 

 also sent some representative specimens of the Deccan traps, 

 which will be analyzed and described later. 



I take pleasure in expressing my sincere thanks to these 

 gentlemen for their courtesy, as well as to Mr. H. H. Hay den. 

 Director of the India Survey, for permission to publish the 

 results of my studies. I have also to thank Drs. H. E. Mer- 

 win and N. L. Bowen, of this laboratory, for their kindness in 



*T. H. Holland, Mem. Ind. Geol. Surv., xxxviii, pp. 121-249, 1900; he 

 cites previous literature. 



■fldem, C. R., xii, Congr. Geol. Int., p. 378, 1914. 

 % J. D. Dana, this Journal (3), xx, p. 194, 1880. 



Am. Jour. Sci. — Fourth Series, Vol. XLI, No. 244. — April, 1916. 



