GEOLOGICAL NOTES ON ASSAM. 31 



The chief interest of the section at Cherrapoonjee, it will be recol- 

 lected, rests upon the close supei-positiou of un- 



Nummulitic and Cre- 

 taceous rocks at Chena- doubted nummulitic strata upon others containing 

 poonjee. 



a fossil fauna of which the facies is cretaceous ; 



no strati graphical boundary having been detected.'^ 



It was of course an object to me_, (and I may say I expected,) to 

 find such a feature. I have, however, failed to do so positively. I can 

 only help to clear the case for future more minute investigation. It is 

 a peculiarly interesting one ; not merely that there is no marked un- 

 conformability, but there are so many features common to the whole 

 series of strata, it will be curious to find where, or whether, paleontology 

 can draw an exact line. Unconformability of a kind can be shown : 

 there is overlap. The many hundred feet of united thickness at Terria 

 Ghat, at the outer edge of the range, is reduced at Mawbelurkar, some 

 twenty miles to the north, to about sixty, all of which may probably 

 belong to the upper or nummulitic group (see below page 37). Still 

 every portion of the series of rocks now referred to undergoes this ori- 

 ginal thinning out ; it is a condition of deposition common to all. Hori- 

 zontal variation in kind as well as in amount of deposition is also common 

 . to the whole. 



Trap rocks form a very remarkable feature in the geology of the 



Cossyah Hills. I have never seen, not even in 

 pre-cretaceous!^^'' ^ Central India, such extensive phenomena of trap- 



pean intrusion. Aware of the important relations 

 of the trap rocks in Western India with nummulitic and cretaceous de- 

 posits, as ascertained last year by Mr. W. T. Blanford, I souo-ht some 

 analogous conditions here, but without the same result. The trap of 

 the Deccan rests upon cretaceous rocks, locally at least, and is older than, or 

 partly cotemporaneous with, the nummulitic. All these strata just refeiTed 

 to as occurring at Cherrapoonjee are younger than the trap, a fact not 



* See Quarterly Journal, Geological Society, London, Vol. XIX., p. 524. 



(417 ) 



