STRATIGRAPHICAL FEATURES. 27 



zontal. On the other hand there is clear evidence that the lavas were 

 subjected to a long period of erosion and weathering before the 

 deposition of the sandstones. In the scarps north of the city of 

 Jodhpur numerous sections of the junction are exposed, in which the 

 sandstones are seen to rest upon a very uneven floor of the lavas. 

 This in itself would not be evidence of unconformability, for the 

 surface of the lava flows was probably originally irregular and 

 hummocky, as is usual with such viscous lavas as these, but the sand- 

 stones can sometimes be seen banked up against denuded and scarped 

 edges of the flows. Moreover, at the base of the sandstones there is 

 frequently a layer of varying thickness in which large blocks of the 

 lava are imbedded in silt and grit (PI. II, fig. 1). These are not water- 

 worn boulders, transported from a distance, but are always of the 

 same variety of lava as that composing the sheet immediately under- 

 lying them, and they have evidently been weathered out in situ, 

 and then quietly buried in silt. Again, the upper portion of the lava 

 flows, where they are exposed beneath the scarps of sandstone, is 

 usually found to be weathered to a considerable depth, so that the 

 lava has become quite soft and rotten. This weathering of the surface 

 of the lavas is not observed where they are not protected by the 

 sandstone, and evidently took place before the latter were deposited, 

 and judging from the effects of atmospheric agencies on the lavas at 

 the present time, it must have taken a very long period to produce 

 the results noted on such slowly altered rocks as these. Lastly, in a 

 few places patches of true conglomerate, containing waterworn and 

 well rolled pebbles and boulders of the lavas, mingled with pebbles of 

 other crystalline rocks, and transported from a distance, are found 

 occupying hollows in the uneven surface of the lava flows, and under- 

 lying the sandstones. These are associated with beds of fine red and 

 green shales also of quite local occurrence. 



Whatever may have been the length of the interval separating the 

 period of the emission of the lavas from that of the deposition of the 



( 27 ) 



