288 RECENT DEPOSITS OF NERBUDDA VALLEY. 



Planorbis Coromandelicus for instance is perhaps one of the common- 

 est shells in India, and yet only one or two specimens have been noticed 

 in the beds of the lower group. Melania lirata. B. M. variabilis. B. and 

 M. spinulosa. Lam ; all common living shells in Bengal, are either so rare 

 as to have escaped detection, or are wanting in these beds altogether, 

 though their congener (M. tuberculata. Mull) occurs fossil plentifully 

 enough. 



These instances suffice. to point out the difference between the fluviatile 

 mollusca of the present epoch and those which existed as cotemporaries 

 of the Hexaprotodon. This difference consists in the greater number 

 of specific forms now living, which preponderance is not compensated for 

 by the occurrence of any extinct forms in the lower group, from which 

 no single species has been obtained which is not abundant in a living state : 

 and though some shells will doubtless have hereafter to be added 

 to the list of fossil species, yet there seems no reason to suppose that 

 any such additions will invalidate the general conclusions above 

 arrived at. 



Above the clay I have been last describing, occur numerous beds of 



sand and gravel, of which no one bed is of suffi- 

 Sands and Gravels. . . . 



cient importance to need special notice. These 

 sands and gravels are usually loose and incoherent, though often bound 

 together by calcareous infiltration into a very hard sandstone or con- 

 glomerate. 



In consequence of extensive denudation which this lower group has 



undergone previously to the deposition of the up- 

 Thickness of beds. 



per beds, the former thickness of these gravels 



cannot now be ascertained, but tbey not unfrequently attain a thickness 



of 20 feet and upwards, especially towards the east. 



Above and below Hosungabad, they occur but sparingly, having been 



nearly entirely removed by denudation ; in that direction patches only 



remaining here and there, as at the mouth of the Tawa nulla above 



