TALCHEER COAL FIELD. 39 



never penetrates into the sedimentary deposits. It seems, however, to 



have aiforded lines of weakness through the gneiss, along which faults have 



taken place subsequently to the deposition of the coal measure beds.* 



The metamorphic rocks of this district may be defined as consisting of 



different forms of gneiss, micaceous, quartzose, 

 Metamorphic bocks. 



and hornblendic,-f- all the forms passing into 



each other and each exhibiting many varieties. The most marked 

 of these, and one which prevails over a very large area, is an almost 

 pure quartz rock, in which the felspar usually present in gneiss has 

 entirely disappeared and mica only remains in very small quantity ; 

 and this is frequently replaced by a talcose mineral. We very rarely find 

 the mica entirely wanting, and even in that case the rock is always 

 distinctly cleavable, by which it is readily distinguished from ordinary 

 quartz rock. Another peculiar form is the hornblendic gneiss, 

 which generally consists essentially of hornblende and quartz, the 

 former being frequently a highly crystalline variety, approaching in 

 character to actinolite, and predominating to so great an extent, 

 that the rock is almost entirely composed of it. 



The micaceous gneiss presents every modification, being fine- 

 grained, coarse-grained, quartzose, &c. &c. Perhaps some such division 

 as follows might be made of the metamorphic rocks ; — 



r { Hard, coarse, compact, and felspathic, be- 



(Var. a.) < coming sometimes lithologically a perfect 



Gneiss. ■{ 



L 



granite. 



(Var. b.) Soft, laminated, quartzose or micaceous. 



c Compact, but sometimes soft, containing garnets 

 (Var. c.) < ^ , , 



I. frequently decomposed. 



* This rock also forms a small hill near Deiuclii in Eehrakol, being there garnetiferous. 

 (A similar rock occurs at Parisnath.) 



t Hornblendic gneiss, meaning gneiss in which the mica is replaced by hornblende, may 

 perhaps not be considered as a correct term ; but the ordinary one, hornblende-slate, 

 would, in the present case, be certainly improper, as the rock is not a slate at all, but 

 a highly crystalline rock, not even cleavable. 



