NERBUDDA DISTRICT. 195 



mical action been most strongly felt. The enclosed fragments (though 

 some of them are of great size) and the edge of the fissure through 

 which the trap apparently escaped upwards, are baked to a porcelain 

 or vitrified ; although the lower surface of the same bed, only a few feet 

 off, where seen resting on the same trap, is quite, or almost quite, unaf- 

 fected by the contact ; nor does any apparent difference in the composi- 

 tion of the rock in the two places suggest the idea that its liability to 



Mineral alteration of Suffer fr0m the acti ° n ° f heat WaS originally dis- 

 the trap. similar. It may be remarked here that differences 



in the texture of the trap itself seem to be equally capricious. In the 

 section just described, the igneous (like the sedimentary rock) seems to 

 be little influenced by the proximity of the super-incumbent mass, which, 

 nevertheless, must be supposed to have had a very different temperature 

 from itself where they came in contact. But elsewhere similar conditions 

 have resulted in very marked changes in the texture of the intruded 

 rock. The upper surface of the trap generally exhibits all the ordinary 

 characters of a dyke wall, becomes less crystalline, often cornean, 

 or even earthy, and divides into thin flakes parallel to the plane of 

 junction. 



Diagram Fig. 6, p. 167, shows another case of the pseudo-interstratifi- 

 cation of the trap and sandstone. Here however the overlying sedimen- 

 tary rock is considerably altered at its lower surface. 



Our examination of this district was necessarily insufficient to prove 

 that no interstratification of the traps and sandstones ever obtained, but it 

 may be safely affirmed that such cases, if they did occur, were exceptional. 

 There are few parts of India which present scenery more picturesque 

 than the Gondwarra Range, included in our map ; the Mahadeva sand- 

 stone is the rock of the country, and its manner of weathering, and the 

 contrast which the ground it covers thus offers to areas, occupied by the 

 softer deposits of the Damuda series combine to form landscapes of the 

 most varied outlines. 



