PROBLEMS OF PETROGRAPHIC CLASSIFICATION 793 



dized decomposition products are exploited. They appear in 

 association with metamorphosed sedimentary rocks of the Khonda- 

 lite Series, other metamorphosed sediments, rich in garnet, called 

 "calc gneisses," a gneissose granite, and the Charnockite Series, 

 the last two being considered of igneous origin. Fermor points out 

 the banded arrangement of all the rocks, the absence of contacts 

 showing intrusive relations, and the closer association of the Kodu- 

 rite Series with the metamorphics than with the igneous Charnockite 

 Series. The only cited occurrences thought by Fermor to indicate 

 intrusive character are in two sections, five miles apart, in which 

 the manganese rocks occupy different relations in metamorphic 

 zones which appear to be made up of the same elements. 



The principal feature of the rocks interpreted as favoring the 

 hypothesis of their magmatic origin is the mineral and chemical 

 composition, which Fermor believes cannot be explained in any 

 other way. 



Before proceeding to review the characters of the rocks I wish 

 to point out that the term "series" is commonly used in India for 

 both metamorphic and igneous rocks as a convenient term by which 

 to group or correlate them as an aid in the analysis of the complex 

 and obscure Archean System. When applied to igneous masses the 

 term has still chiefly a stratigraphic sense, is used for convenience, 

 and is subject to free modification. "Kodurite Series" is applied 

 by Fermor to rocks assumed to have common origin through 

 differentiation, but this view is not as yet justified by chemical 

 investigation or adequate knowledge of relations and the name 

 appears to be simply a practical, justifiable term of convenience 

 for local uses. 



The Kodurite Series consists of quartz-orthoclase rock, apatite- 

 quartz-orthoclase rock, quartz-kodurite, orthoclase rock, kodurite, 

 pyroxene-kodurite, biotite-kodurite, spandite rock, apatite-spandite 

 rock, pyroxene-span dite rock, manganese-pyroxenites, and graphitic 

 manganese pyroxenites. These varieties and the intermediate 

 phases have not been described as yet in a connected manner show- 

 ing the chain of pecuhar characters necessary to establish a true 

 petrographic series. But few chemical analyses are offered by 

 Fermor. 



