?6 HATCH : THE KOLAR GOLD-FIELD. 



gneiss from the same locality (see p. 75). It is placed here as it is reported to be 

 within the Dharwar boundary, and the other is placed with the gneiss out of 

 respect to its petrological similarity to the latter rocks. These two types, there- 

 fore, give us stages in a petrological transition from the quartzites to the gneiss ; 

 but the actual relationship is not probably so simple. Had the underlying 

 granite-gneiss presented an intrusive relation with regard to the Dharwar schists, 

 this transition band might be regarded as an example of the contact phenomena. 

 But all the field workers agree unanimously in regarding the Dharwar schists of 

 Kolar as younger than the granite-gneiss, and besides recounting the unmistak- 

 able nature of the evidence at Kolar, Mr. R. Bruce Foote has cited numerous 

 instances from other areas to show that Newbold was mistaken in supposing that 

 the granitoid gneiss in South India intruded into his " hypogene schists 

 (Dharwar). 1 



The apparent transition of the mica schist into the gneiss must be due, therefore, 

 to the alteration of both classes of rocks — a kind of welding process— during the 

 subsequent metamorphism which affected both, but to which the granite-gneiss 

 yielded only at its marginal portions. The instance here of a mica schist and a 

 highly crushed (schistose) mica-gneiss near the base of the Dharwars, resembles 

 to a certain extent the Nemkal section in the Bellary district described by 

 Mr. Foote, 2 who does not appear to suspect in it any indications of the granite- 

 gneiss being intrusive. 



It would be interesting to find out if the occurrence of mica schist is always 

 limited to a lower stage in the Dharwars ; it is frequently the case, and it is this 

 petrographical contrast— hornblendic schists on the one hand and mica schist on 

 the other — which serves to distinguish the Dharwar series from the so-called 

 " upper gneisses " of Peninsular India. The contrast is one which holds 

 elsewhere, particularly in America, between the corresponding series, for instance, 

 the Keewatins and the Coutchichings of Canada. Because of the remarkable 

 quiet which has been enjoyed by Peninsular India for so many geological ages 

 every fact of this kind in connection with our azoic rocks will have more than 

 local value. 



d. Quartzites and Quartz-iron-ore Rocks. 



The term quartzite is applied to the rocks composed largely of granular quartz, 

 but none of the Kolar specimens shows the slightest structural evidence of detrital 

 origin. They agree in all essentials with the ferruginous quartzites which so 

 frequently form prominent ridges amongst the so-called Transition Rocks of South 

 India. 



1 Cf. R. Bruce Foote, " Geology of the Bellary District." Mem Geol. Surv. Ind., Vol. 

 XXV, pp. 22, 28, 137 and 139. [Since the above was written I have been informed that the 

 Mysore Geological Department has recently distinguished three types of granite-gneiss in the 

 neighbourhood of the Kolar field, and one of these appears to be younger than the Dharwars. 

 From specimens, however, sent to represent the three different types (whose relations are 

 shown on the geological map), I am unable to detect any essential petrological distinctions. 

 The divisions of the granite-gneiss presumably, th-refore, rest on field evidence.] 



2 Mem. Geol. Surv. Ind., Vol. XXV, p. 147 and plate vi. 



