STRATIGRAPHY. 13 



and it is more than probable that the boundaries as mapped do not 

 represent isochronic divisions. That i« to say, beds which in one 

 section have, on account of their lithological character, been mapped 

 in one stage may be contemporaneous with beds that have, in other 

 sections, been mapped with those of a contiguous stage. 



The lowest of these is that which has been called basal. It 

 consists of sandstone and conglomerate at the 



Basal stare. , . . . . . . , 



bottom, overlaid by a varying thickness of 

 shales and limestone. Of all the stages it shows the greatest and 

 most rapid variations in thickness, and this is especially prominent 

 in the lowest beds of all. These usually consist of sandstones and 

 pebbly sandstones of the same type and character as those at the 

 base of the red shale series, and were evidently formed in a similar 

 manner. On some sections these rocks attain a thickness of 

 four or five hundred feet and then form a conspicuous ridge, such 

 as that which marks the boundary of the lower Vindhyans from 

 Marai to the neighbourhood of Samaria. In the eastern outlier, 

 near Tarka, the conglomerate is replaced by an angular breccia, 

 which is evidently an old talus deposit, the disintegrated rock on 

 and at the foot of the old hill-sides having been covered up by 

 subsequently added deposits without having been washed away or 

 sorted by stream action. 



Above the sandstone there comes, at the eastern end of the 

 area on the map, a massive limestone which attains a thickness 

 of some 300 to 400 feet about Agori. In the central and western 

 parts of the area a band of limestone sometimes overlies the 

 sandstone and at places there are thin strings of siliceous limestone 

 in the sandstone, but as a rule the rock immediately above the 

 basement beds is a fine-grained shale, often as fine-grained and 

 soft as is to be found anywhere in the whole thickness of the lower 

 Vindhyans. 



These shales are capped, in the neighbourhood of Marai and 

 Deora, by a conspicuous band of limestone, which is cut off by a 

 fault ,to the west and disappears by thinning out to the east. 



( 13 ) 



