6 HATCH : THE KOLAR GOLD-FIELD. 



east of the Coromandel Mine) a remarkable rock, having the appear- 

 ance of a conglomerate, outcrops. Imbedded in a fine black horn- 

 blende matrix, in which a marked pseudo-flow structure is perceptible, 

 are sub-angular a boulders," "pebbles" or fragments of a granitic 

 rock. A striking feature is the often elongated or rod-like form 

 and rude parallelism of the fragments and further their tendency 

 to tail off into streaks and veinlets of pegmatite or quartz. The 

 tendency to elongation has been ascribed in other Dharwar con- 

 glomerates to a deformation of the pebbles j 1 but it appears almost 

 certain that at Kolar the reverse is the case, namely, that the pseudo- 

 pebbles have been formed by the deformation of granite veins occur- 

 ring in a schistose rock ; or, in other words, that we have here to do 

 with a fine example of dynamic or autociastic conglomerates, similar 

 to those described by Barlow 2 and others as occurring among 

 Archaean rocks in Central Ontario. According to Barlow " the 

 supposed conglomerates were in reality autociastic rocks and the 

 so-called pebbles extremely deformed portions of a series of more or 

 less parallel dykes, evidently highly differentiated apophyses of the 

 neighbouring plutonic mass." This explanation of the origin of the 

 supposed conglomerates seems quite applicable to the present case. 



The hornblende schists which make up the bulk of the Dharwar 

 formation at Kolar consist mainly of altered trap-flows of basic 

 composition and as such may be termed epidiorites. Under the 

 microscope several good examples of well-defined ophitic structure 

 such as characterize diabase rocks are found ; but, of course, the 

 original augite has in every instance been completely altered to 

 green uralitic hornblende. The felspars retain their original lath- 

 shaped character, but their substance is altered to a granular aggre- 



1 Manual of the Geology of India, 3rd edition, p. 49. 



2 A. E. Barlow " On the Origin of some Archaean Conglomerates." Geological 

 Society of America. New York, December 28, 1898. See also Van Hise, 16th 

 Annual Report, U. S. Geological Survey, pp. 679, 894.-95. 



The term " autociastic " is defined as applicable to rocks which " have formed 

 in place from massive rocks by crushing and squeezing without intervening 

 processes of disintegration or erosion, remgval, and deposition. " 



