MEMOIRS 



OF 



THE GEOLOGICAL SURVEY OF INDIA, 



The Mica Deposits of India, ^Thomas H. Holland, 

 A.R.C.S., F.G.S., Officiating Superintendent, Geological 

 Survey of India. 



I.-INTRODUCTION. 



The primary object of this paper is to describe the Indian 

 occurrences of mica commercially valuable. As this last expression 

 implies mica-crystals of a certain size and without the flaws usually 

 and easily produced by earth-movements, the geologist will readily 

 see that the ground to be considered must of necessity be very limited 

 in extent. Such an area must be one from which the sedimentary 

 mantle has been completely removed and on which denudation has 

 been sufficiently thorough to bring the deep-seated plutonic rocks 

 to the surface, an area, too, which has escaped all tectonic movements 

 since the formation of its pegmatites ; for mica, being the most delicate, 

 is amongst the first of rock-constituents to suffer deformation from 

 crust disturbances. Occurrences combining these characters are 

 necessarily few and comparatively restricted in extent, and for such 

 reasons the available mica supplies of the world are strictly lim- 

 ited—a fact of the highest concern to the country which happens 

 to possess an area so large and geologically so suitable that it is likely 

 to have the means of controlling, if not of actually monopolising, the 

 B ( i ) 



