GENERAL CONSIDERATIONS, 195 



position by intrusion. Even if we reverted to the old idea that all 

 these rocks are regionally metamorphosed sediments, the inter- 

 banded charnockites could not be older than the magnetic iron- 

 ore beds, for the latter occur below as well as above the former. 



Unfortunately, the question of greatest importance — the petro- 

 logy of the Dharwar conglomerates— is the subject about which 

 we are still most ignorant. Pebbles of " schist, quartz, quartzite, 

 grit, banded hornstone and gneiss n have been referred to in con- 

 nection with these conglomerates, but their microscopic characters 

 have not been described. Recently, through the kindness of Dr. 

 J. W. Evans, State Geologist of Mysore, we received pebbles from 

 a Dharwar conglomerate which occurs in the Kolar Goldfield. 

 Microscopic examination of these shows them to be indistinguish- 

 able from the old biotite-gneiss which is corroded by tongues of 

 the charnockite series near Salem {vide infra, p. 226). From these 

 facts we conclude that the charnockite and the particular Dharwar 

 conglomerate from which these pebbles were obtained are both 

 younger than the biotite-gneiss near Salem, but we still have no 

 clue as to the relative ages of the Dharwars and the charnockites. 

 It is to be hoped that every effort will be made in future to collect 

 and identify pebbles from the lower Dharwar conglomerates with a 

 view to the elucidation of this important point. 



Although we have no clear proof of their antiquity, we must 

 be prepared for the conclusion that the charnockites are quite old 

 enough to have suffered from the tangential pressures which have 

 left their mark so plainly on the highly folded Dharwar strata. 

 Under such circumstances, the preservation of so much pyroxene 

 would require explanation. 



Concerning the anorthosites of Canada, which have much 



stability of pyroxene in common with some forms of the charnock- 

 at high temperatures. Ue Berie ^ Adams has made some very sugges- 

 tive remarks about the stability of the pyroxene during the granulation 

 which is sometimes carried far enough to produce a thorough « Rutsch- 

 mehl." " The cataclastic structure is not," Adams says, " developed 



( 77 ) 



