209 



To palaeontologists then, we may now announce that a most interest- 

 ing case awaits their investigation, namely, the comparison of well 

 represented vertebrate faunae, occurring in a series of beds, closely 

 related in point of geological conditions of deposit, etc., and yet 

 distinctly separated (broken) in time. 



The application of the fact to stratigraphical geology may now 

 take shape. The strata at the base of the sections visible in parts of 

 the Sivalik hills are representatives of the Nahun group — the middle 

 group of the Sub-Himalayan series. The expression of this on a map 

 must still be arbitrary : for the true Sivalik strata (though so strongly 

 unconformable with the ( Nahun' strata along their junction with the 

 inner zone of these Nahun rocks,) appear to pass conformably and 

 even by gradation into the representatives of the Nahun strata in the 

 outer zone. It is of course to be expected that a very close study 

 will reveal traces of this unconformability in the sections of the 

 Sivalik hills also ; but in such massive, banked strata, from twenty to 

 two hundred feet thick, the determination of such a feature will be 

 very dubious. 



In physical geology this feature will be only another example, on a 

 larger scale than those given in my Memoir, of the supposition I have 

 offered in explanation of the mode of disturbance of all these Sub- 

 Himalayan rocks— slow contortion and upheaval along narrow zones, 

 synchronously with more or less uninterrupted deposition in the ad- 

 joining exterior area. 



