_?44 HOLLAND: CHARNOCKITE SERIES. 



charnockite series, and apparently of foreign origin, have 

 been found included in these rocks, and are regarded as 

 xenoliths picked up and altered by the charnockites. 



(6) In chemical composition the ordinary members of this series 



have their nearest equivalents amongst known igneous 

 rocks, and from the chemical evidence they would be class- 

 ified with Rosenbusch's or tho gneisses. 



(7) Mineralogically the basic and ultra-basic types are precisely 



similar to the igneous norites and pyroxenites; the acid 

 and the common intermediate types correspond in general 

 to enstatite-granites and pyroxene-diorites respectively, 

 though these, especially the former, are too rare to permit 

 general comparisons. 

 The evidences by which the origin of a rock mass is determined 

 naturally suffer partial obliteration by subsequent geological changes, 

 and in consequence of their great age some of the phenomena referred 

 to above are not as simple and straightforward as would be expected 

 if these rocks had invaded younger sedimentary formations. Al- 

 though, however, each point of evidence would alone be insufficient 

 to prove the igneous origin of the charnockite series, the consistent 

 agreement of all the ordinarily recognised tests— direct and by ana- 

 logy — i s far too striking to be overlooked. No evidence, more- 

 over, has been discovered which is definitely inconsistent with our con- 

 clusions as to the origin of these rocks, though there are some features 

 which are sufficiently unusual in normal igneous rocks to demand a 

 special explanation. For instance, — 



(1) The persistent granulitic structure and the almost constant 

 absence of pronounced porphyritic crystals is remarkable 

 for such large masses of igneous rocks. Similar features 

 have, however, been noticed as persistent characters of 

 the gneissose elseolite-syenites of Coimbatore, the anor- 

 thosites of Bengal and the norites of Coorg — rocks whose 

 igneous origin it would be ridiculous to question. Stages 

 ( 126 ) 



