GEOGRAPHICAL DISTRIBUTION. 49 



no stratigraphical sequence can be established amongst these schists, 

 and their value is appraised simply by their interest as lithological 

 types. A list of those so far recognised in the Indian mica-bearing 

 tracts is given in Chapter II. Practically the whole of these occur in 

 the Behar mica belt, and some of them have been recognised only in 

 this area, which has had a more thorough examination, and is better 

 dissected by atmospheric agents, than the other mica districts of India, 



In his survey of this belt, Mr. Mallet distinguished three stages 

 amongst the schists, an upper stage composed of quartzites as seen in 

 the Mahabar hill, a thick middle stage in which mica-schists largely 

 predominate, and a basal member in which quartzites again prevail, 

 and, as in the Bhiaura ridge, are sometimes very strongly developed. 

 Mr. Mallet was compelled by the general theory then prevailing to 

 regard these rocks as younger than the associated "dome-gneiss," 

 yet, with characteristic faithfulness, he recorded numbers of facts 

 giving no support, and, in negative evidence at least, often conflicting 

 with, his interpretation of the phenomena. His map, which is a 

 remarkable piece of patient skill, shows a very intricate boundary 

 between the schists and the dome-gneiss, whilst he states that the 

 foliation planes in both rocks are found to follow the intricate twist* 

 ings of the outline. The formation distinguished by him as the 

 lowermost member of the schist-group is shown on the map as a 

 narrow mantle wrapped around each protuberant mass of dome-gneiss, 

 Microscopic examination of this mantle reveals far more than quart- 

 zitic rocks as they so often appear to be in hand-specimens : it displays 

 many phenomena characteristic of igneous contact, and with the con- 

 clusion that the " dome-gneiss " is in reality an intrusive granite, 

 younger than the schists, these phenomena at once become intelligible, 

 and the difficult facts mentioned by Mr. Mallet are explained. 



Accessory minerals. — In a few places minerals of economic 

 value other than mica occur, and in some cases might be made accessory 

 to the mica industry, though probably none of them is sufficiently 

 abundant to found independent industries. The oxides of iron occur 

 in quartzcse schists similar to those better known in the South of India, 



( 39 ) 



