AVIFAUNA OF CHOTA NAGPUR. 365 



In this region too we find plateaus with a base of these sand- 

 stones covered by basaltic trap, and capped, in some cases, by 

 several hundred feet of laterite. 



This trap belongs, it is considered, to the age of the great 

 Dekan flows, the nearest point of which at Umerkantak is indeed 

 not very far distant. No fossils have as yet been found in the 

 beds of shale, which occur between the successive flows of this 

 trap ; but if the identification, by mineralogical and other more 

 general considerations be correct, then these rocks belono- to 

 the upper cretaceous period. 



Some of the flows of this trap have a columnar structure, 

 which give a very marked character to the scenery of the 

 ravines which are cut down through the sides of the 

 plateaus. 



I have above mentioned the laterite; it not only caps the 

 plateaus and hills of Western Chota Nagpur, but is also found 

 along the eastern frontier stretching thence southwards into 

 Midnapur. 



The origin of this remarkable formation is still unsettled. No 

 theory yet proposed has been able to account for the sources 

 from w T hence the iron, which is its most characteristic consti- 

 tuent, has been derived, and no fossils, from which the conditions 

 under which it was deposited could be determined, have been 

 discovered in it. 



Of the alluvium and other recent deposits but little need be 

 said here. On the east the boundaries of the rocks, where they 

 dip under the alluvial plains of Bengal, nearly coincide with 

 the limits of the Division. 



Within our limits the deposits of alluvium are, for the most 

 part, due to the locally adjacent rivers. The alluvium of the 

 Damuda valley, and in a less degree that of some of the 

 other rivers, abounds in kankar or guiin, which is the well- 

 known source of the only lime available in many parts of 

 India. 



The interdependence between the geology of a country and 

 its Fauna is much more real than is apparent to mere casual 

 observation. The connection is mainly, though not exclusively, 

 established through the medium of the Flora. Certain soils, the 

 result of the disintegration of certain rocks, are favorable to 

 the growth of particular plants, which in some cases support 

 special forms of animal life. 



The tracing out of these cycles is the pleasing duty of the 

 naturalist. But all such generalisations are dependent upon 

 the accurate determination of species. 



