GENERAL GEOLOGICAL DESCRIPTION OF THE FIELD. 7 



gate of secondary minerals. In a few cases the felspars are of a 

 porphyritic character occurring in longish crystals with well pre- 

 served rectangular boundaries. Ilmenite or titaniferous iron-ore, with 

 its accompanying alteration-product — leucoxene, is plentifully dis- 

 tributed in many of the rocks. In the near neighbourhood of the 

 quartz lodes a characteristic brown mica is abundantly developed, 

 and so much so is this the case that its plentiful occurrence may be 

 regarded as an indication of the near presence of a lode. It appears 

 probable that this brown mica is genetically connected with the 

 mineralization of the lodes, whether by vapours from below or by 

 ascending mineralizing solutions. 1 While touching on this point it 

 may be pointed out that the suggestion made by Dr. W. J. Evans 2 

 that the quartz lodes of the Kolar gold-field are not veins, but 

 interbedded seams of true metamorphic quartzite of similar origin to 

 the Witwatersrand beds of the Transvaal, must be rejected. There 

 is not the slightest indication of such an origin or of any resemblance 

 to the Rand conglomerates. The Kolar deposits are typical quartz 

 veins and can only be termed bedded in so far that the quartz has 

 been deposited from mineralizing solutions along the foliation planes 

 of the schists in which they lie. 



In addition to true epidiorites, i.e., hornblende schists, which are 

 undoubtedly derived from basic igneous rocks of diabasic character, 

 there are others in which no igneous structure is apparent and which 

 Mr. Holland suggests may possibly be derived from basic ash beds 

 associated with the trap-flows. 



The latest rocks in the geological tract under description are 

 the basic dykes which traverse the schist belt and granitic rocks, 

 generally transversely or east and west, but also occasionally north 

 and south. These dykes vary in width from a few feet up to over 

 a hundred feet and are frequently encountered underground in the 



Mr. Holland suggests (vide appendix) that the brown mica has been pro- 

 duced by deep-seated vapours attacking the hornblende and supplying the 

 requisite amount of water and alkalies. 



2 Rec. Geol. Surv. Ind., Vol. XXIX (1896), p. 82, and Vol. XXX (1897), 

 p. 2. 



