194 HOLLAND : CHARNOCKITE SERIES. 



comes home to us, for the charnockite series are assumed to be 

 Archaean. 



Before this enquiry can be satisfactorily undertaken there are 

 several points on which further information is essential. In the first 

 place, the lower limit of the Dharwars is not sufficiently defined to 

 warrant the assumption that all the Dharwars are younger than all 

 the Archaean gneisses and schists. In other words, the break between 

 the biotite gneisses and the Dharwar rocks, which Mr. Foote recog- 

 nised in the Bellary District, has only a local value. 1 No unconfor- 

 mity has so far been found between the charnockite series and the 

 Dharwars. On the other hand, members of the charnockite series 

 occur as lenticular masses or bands associated with ferruginous 

 quartzites which do not differ greatly from the ferruginous quartzites 

 so abundant in the lower stages of the Dharwar system. The ferru- 

 ginous quartzites referred to are those which occur so frequently in 

 the central and southern districts of the Madras Presidency, Kanja- 

 malai and Godamalai being conspicuous and well known examples in 

 the Salem District for instance ; these rocks are composed of 

 magnetite, hematite, and quartz with a pale-green hornblende, 

 and they only differ from the rocks of similar mineral composition in 

 typical Dharwar areas in their more perfect crystallization and 

 in, perhaps, the predominance of magnetite over hematite — points 

 which merely indicate differences in degree of metamorphism, not 

 necessarily differences of age. 2 As far as these magnetic iron-ore 

 beds are concerned, there is not the slightest reason for considering 

 them to be younger than the charnockite series. On the contrary, if 

 our views as to the origin of the charnockite series are sound, it is 

 more likely that the latter are younger and have attained«their present 



1 Manual of Geology of India, 2nd edition, pp.49, 50 ; R. B. Foote: "The Geology of 

 the Bellar District, " Mem. Geol. Surv. Ind., Vol. XXV (1895), pp. 28, 74. 



2 The suggestion that these southerly iron-ore beds are merely altered outliers of Dharwar 

 age has been made in a separate memoir descriptive of the rocks in the immediate neighbour- 

 hood of Salem (Mem. Geol. Surv. Ind., Vol. XXX, part 2). The discovery of laYge pro- 

 portions of hematite in the magnetic ores of the south and of magnetite in hematitic ores of 

 the Dharwars considerably reduce the previously recognised differences between the two 

 groups of rocks. 



( 76 ) 



