GEOLOGY OF CENTRAL INDIA. 



occur, and in some instances this rock assumes an almost schistose 

 aspect. When this last is broken in a direction parallel to the schistose 

 structure, minute scales of mica may be frequently observed, which 

 divide the mass into a number of thin parallel bars. The mica can- 

 not be observed in the unbroken mass, or in the cross fracture, and 

 the bars are sometimes so thin that the rock assumes a fibrous ap- 

 pearance. 



When felspar occurs associated with hornblende, the former is gene- 

 rally white or grey, and in some specimens of sienitic granite, I have 

 observed that the felspar, when exposed at the surface, has acquired 

 a reddish tint, and it is only on breaking the mass that we discover its 

 real color. In one hand-specimen, broken from the junction of a horn- 

 blende rock approaching to sienitic granite, and a close-grained granitic 

 rock, through which are disseminated minute yellowish green specks of a 

 mineral, which appears to me to be Epidote, — the felspar of the hornblende 

 rock is grey, while that of the other is reddish ; the felspar acquiring a 

 redder tint in proportion as it is removed from the hornblende. Through 

 many of the granitic rocks which occur here, the minute green specks just 

 alluded to, are disseminated. When these rocks are exposed to a powerful 

 heat, the green color of these specks is converted into a black, and a 

 similar mineral occurs intimately associated with a rock which appeared 

 to me, on first seeing it, to be a variety of a schistose quartz. It has a 

 specific gravity, however, varying from 2-9 to 3-4, or even 3-5, according 

 as this green mineral is in larger or smaller proportion. This last ap- 

 pears to be translucent at the edges, to have a fracture slightly foliated, 

 and something of a fibrous structure. Its hardness is intermediate, 

 between that of felspar and quartz — it is rather brittle, and before the 

 blow pipe, or when exposed to a powerful heat, it is converted into black 

 or dark brown scorioo. Its color is light yellowish green, and sometimes 



