362 AVIFAUNA OF CHOTA NAGPUR. 



, Whether the successive layers of different mineral com- 

 position are coincident with original beds of deposit, or are 

 the result of a superinduced structure — a sort of foliation 

 on a large scale — has not been finally agreed upon. If, 

 however, these layers do correspond with the original bedding, 

 as seems to me to be probable, then the thickness of the 

 whole series must be very considerable, but from the 

 difficulty of ascertaining either the base or summit of the 

 succession it is impossible to make any conclusive measure- 

 ment. 



These rocks are in some localities much traversed by veins of 

 quartz and granite, and in places by systems of trap dykes. A 

 remarkable instance of the latter may be seen in the central part 

 of Singhbhum where there are several series of intersecting 

 dykes. 



Except in Sirguja and the lower part of Manbhum all the 

 loftiest plateaus and most of the hills are formed of these 

 metamorphic rocks. 



Resting upon these, the oldest primary rocks, is a perfectly 

 distinct seines of metamorphosed beds, which seem to have been 

 subjected to a less amount of the metamorphosing influences, 

 and are accordingly spoken of as the sub-metamorphics. The 

 series consists of quartzites, micaceous and magnesian schists, 

 trappoid rocks, slates and limestones. No variety of gneiss is 

 found in it. * 



This series, within our limits, is most strongly developed in 

 Manbhum and Singhbhum, whence it stretches westwards into 

 Gangpur. It is found also in Sirguja. Some of the rocks 

 show little sign of metamorphism, and on the whole in this case 

 it is impossible to believe that the layers showing different 

 mineral composition do not correspond with the original 

 bedding. 



The alternations in mineral composition of the rocks of this 

 series make a very visible impress on the physical features. 

 The tougher varieties, schists or quartzites, stand out in relief, 

 while the softer argillaceous slates are worn down into hollows. 



These rocks are generally much richer in ores of the metals 

 than are those belonging to the preceding series. Among these 

 ores those of iron, copper and lead may be enumerated ; while 

 native gold is found in the river sands throughout, and according 

 to my experiments in much greater quantity than it occurs in 

 areas occupied by the metamorphic rocks. 



The magnesian schists and potstones are largely used in 

 the manufacture of plates, bowls, aud images for temples. 



