160 FOOTE: GEOLOGY OF THE BELLARY DISTRICT. 



Archaean granites and gneisses long before the commencement of 

 the Dharwar era. 



No striking dissimilarity in external appearance was noticed, 

 except in one special case, between the rock material of the dykes 

 unquestionably intruded in post-Dharwar times and those which 

 appear to belong to the pre-Dharwar era. Whether a close petro- 

 graphical and microscopical examination of all the dykes will allow 

 of such age difference being determined in this way, is a question 

 remaining to be answered by further research. The special case 

 mentioned above, in which marked dissimilarity of character of the 

 rock was noticed, is that of a group of dykes penetrating the 

 Dharwars of the Penner-Haggari band in the valley of the Haggari 

 river, which is described further on (p. 164). 



The number of dykes noted as cutting the Dharwar rocks is 36, 



Number of post- of which three are possibly doubtful, and may 



Dharwar dykes. prove possibly to be of pre-Dharwar age, which 



formed high upstanding ridges, around and over which the Dharwar 



rocks were deposited on the surrounding old archaic surface. 



Only the large or otherwise important members of the number 

 will be named separately ; and in considering them, it will be most 

 convenient to take them serially from west to east. 



Of the dykes cutting the Dharwar rocks in the Kunchur tract 

 Dykes in the Kun- °f tne Shimoga band, one of the largest, and at 

 chur tract. ^ e same time one of the most interesting, is 



that which runs north-west towards Holal from Tharada and con- 

 tains included masses, which appear to be fragments of the granitoid 

 it was protruded through. 



Another great dyke which lies some five miles to the north-east of 

 Holal and passes close west of the village of Virapur, is deserving 

 of some little notice from the intense blackness of the surface rocks, 

 and their rather scattered and detached arrangement along the strike 

 of the outcrop which, but for the unconformity of the argillites 

 it passes through, might well be mistaken for a narrow flow- 

 outcrop. 



( 160 ) 



