ARCH/EAN AND PLUTONIC ROCKS. 31 



An examination of the Archaean rocks of the Bellary and adjacent 

 Question of the origin districts, in which exceedingly granitoid forms 

 of the Archaean rocks. predominate so largely, at once raises the ques- 

 tion of their origin — whether they are old Plutonic rocks in which 

 pressure and contortion have induced in some parts a pseudo-bedded 

 structure, or whether they are simply very ancient sedimentary form- 

 ations, which have been locally extra-affected by regional metamor- 

 phism continued for longer periods and to a greater extent than in the 

 case of their equivalents in other parts. The phenomena displayed 

 by the rocks themselves appear at some places to favour the first, and 

 at others the second, hypothesis, and it is extremely difficult, in fact 

 practically impossible, to decide by mere macroscopic study of the 

 rocks which hypothes is to favour. The immensely granitoid structure 

 prevailing, almost exclusively, over such large areas favours the first 

 hypothesis, while the remarkable parallelism subsisting between the 

 strike of the bedding and the strike of the great bands of different 

 mineral constitution which traverse the country, such as the Bellary, 

 the Kapgal, the Alur, the Adoni,and the Yemmiganur bands to the east 

 of the Sandur synclinal, and the Chornur, Kudligi, and Harapanahall, 

 bands to the west of it {vide pp. 2 to 7), certainly favour the second 

 hypothesis. It remains to be seen whether the problem will be solved 

 when the microscopic investigation of a large number of specimens 

 from the different rock bands shall have been completed. Till then 

 at least the subject will remain sub judice. My personal convic- 

 tion tends more and more to the hypothesis that the Bellary grani- 

 toids and their representatives are really old Plutonic rocks arranged 

 in bands— flows, in fact, of old acidic magmas modified by the im- 

 mense lateral pressure they underwent during the crumpling period, 

 after the formation of the Dharwar rocks system. 



The most notable fact concerning the general distribution of the 

 crystallines is the general persistence of the strike of the bedding, 

 which is mostly from south-east to north-west, and shows but few 

 variations from that direction, and none of them extending over any 

 great areas. Hardly any of these are of sufficient importance to be 

 referred to separately. 



( 3i ) 



