212 HOLLAND: CHARNOCKITE SERIES. 



and internal structures recognisable in the field, and, (2) its micros- 

 copical and chemical characters. 



With younger, undisturbed, igneous masses the field relations 

 of the rocks offer more direct and reliable evidence, whilst with the 

 crystalline schists the field characters are more often destroyed and 

 the question of their origin is then based on their microscopical and 

 chemical resemblances to known igneous types : the argument is 

 thus reduced to mere analogy. With many formations in crystalline 

 areas the microscopical and chemical evidences are all we get or can 

 ever expect ; but with the charnockite series we have very straight- 

 forward field evidence in favour of their igneous origin, and this 

 circumstance we have to attribute to the remarkable state of quies- 

 cence, as well as the uninterrupted and prolonged denudation, 

 which has characterised Peninsular India for many geological 

 ages. On this account it is less surprising to find features pre- 

 sented by the charnockite series which have never been noticed in 

 the case of the pyroxene-granulites and related rocks in other parts 

 of the world, where they have been subjected to repeated and 

 intense dynamic metamorphism, or insufficiently uncovered by de- 

 nuding agencies. 



Field Characters of the Charnockite Series. 



The geological features which indicate the igneous origin of the 

 charnockite series may be conveniently classified as follows : — 



(a) Form and structure of the great massifs. 



(b) The existence of dykes and apophyses proceeding from 



the main mass through adjoining formations. 



(c) Contact metamorphism of the surrounding rocks. 



(d) Inclusions of older foreign rocks and the changes they 

 show. 



The first of these four points forms an argument based purely on 

 analogy : we are acquainted with the usual external form and 

 internal structures of known eruptive masses, and the presentation 



( 94 ) 



