NOMENCLATURE. 13! 



So too with the structures : the charnockite series occur in 

 dykes and in bosses ; they show basic schlieren, acid contempo- 

 raneous veins, primary breccia and other structures peculiar to 

 igneous rock masses, and include foreign bodies (xenoliths). 



But unless a similar formation found in another country, can be 



proved to be a genetic relation of the typical 



The name charnockite exposures described in this paper, it is hoped 



limited to this province. . 



that the name charnockite will never be used out- 

 side India. The name is applied to a definite member of a very 

 definite petrographical province now exposed in India, and unless out- 

 siders give it a wider application than that now proposed the terms 

 charnockite and charnockite series need never become a burden to 

 petrographical nomenclature. Charnockite is a convenient name 

 for a quartz-felspar-hypersthene-iron-ore rock in the charnockite 

 series, and not a name for any hypersthene-granite occurring in 

 other petrographical provinces. The much-complained-of burdens 

 of petrographical nomenclature are not due to the creation of speci- 

 fic names for local types, but to irresponsible and unwarranted 

 extension of such names to include unrelated members of different 

 and widely separated petrographical provinces, in which the accidents 

 of differentiation and segregative consolidation may have produced 

 by chance similar mineral aggregates. 



The charnockite series belong to a very old petrographical 

 province, so old that we have no present reason for separating them 

 from the Archaean " group ;" but still young enough to show their 

 intrusive relations to older Archaean formations. During the great 

 lapse of time since the production of the very old geological forma- 

 tions — whether sedimentary or eruptive— secondary changes have 

 tended to remove many of the primary peculiarities of rocks, and have 

 induced the development of a resemblance between genetically dis- 

 tinct types ; so that there is always a danger of including unrelated 

 formations when delineating the boundaries and distinctive characters 

 of a very ancient petrographical province. It is possible, therefore, 

 that we maybe including under the name "charnockite series" 



( '3 ) 



