36 GEOLOGICAL NOTES ON ASSAM. 



irregular texture.* I noticed in it some of tlie large angular grains of 



felspar that are so largely distributed in tlie bottom-rock. Below 



Mawmluh a dark green, fragile rock is higbly fossiliferous. In the inner 



gorges of the hills the sheer scarp is higher than along the outer range, 



and includes both the lower bands of strata. It would seem to be the 



great development of the middle shales along the southern zone that 



has caused the scarp there to terminate with the bottom-rocks. 



The upper group also is physically well defined. It forms the 



well scarped hills rising from the plateau to the 

 Upper group. t n r^i 



south-west of Cherra. It consists of fifty to 



eighty feet of pure limestone, covered by sandstones, shales, and coals, 



all being intimately associated. The top limit is a denuded surface. 



The variations in this band are as marked as in the preceding; the 



limestone and the coal are frequently wanting. These are the rocks 



definitely known as nummulitic. In seeking for a strati graphical 



boundar}^ corresponding to the change in the fossil fauna, one is naturally 



led away by the very marked physical feature at Cherrapoonjee. I 



could not find any sufficient confirmation of this suggestion. Unbroken 



sheets of the Cherra sandstone pass under the nummulitic rocks. 



Any irregularities that appear in it fall well within the natural conditions 



of deposition of such a rock. The sandstones above and below the 



limestone exhibit no characteristic difference^ so that when the limestone 



is absent, this boundary would become imaginary ; as north of Cherra, 



where the sandstones, with the coal, form part of the general scarp ; 



the feature at Cherra being quite' local. This question of a boundary 



^ . , , . , seems to come to a crisis northwards : as at 



Crucial sectionat ' 



Mawbelurkar. Mawbelurkar, ten miles from Cherra, where a rock 



apparently representing the very bottom of the whole series is associated 

 with those of the topmost horizon ; the total thickness being under one 

 hundred feet, while on the outer sections it has been estimated as two 



* Mem. Geological Survey, lud'ui, Vol, I., p. 118, &c. 



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