GEOLOGICAL NOTES ON ASSAM. 33 



tlie sedimentary strata^ gives an ajiparent suggestion of some connection 

 with the local subjacent rock. Some beds are almost entirely made up 

 of such matter,, and assume a spheroidal structure very like a trap rock. 

 This may^ however, be altogether deceptive. I did not observe any detrital 

 matter in these rocks that could he positively/ identified as trappean. 



I would draw the attention of future observers to any connection 

 „ .,, , ,. ,,, that may exist between the central trap and the 



Possible relation of the ^ 



trap to the granite of granite of Molim. I was g-reatly struck bv the 



Molim. o ^ J 



similarity of the relation of both to the quartzite 



sandstones of Shillong. At various points of the boundary from the 



south of Shillong, by Mawreng, to Lailangkot, the contact is very well 



defined. The coarsely crystalline granite comes close up to the stratified 



rocks, which are not marhedly more altered than elsewhere, whether in 



a schistose form or as quartzite, both granular and compact. The beds 



observe no regularity, dipping to and from the granite at moderate 



angles, or abutting obliquely against it. About the centre of the granite 



area, south of Molim, I noticed some fine-grained, and even some 



sub-compact, trappoid masses. At a short distance west of Lailang-kot 



the dense trap occurs in force within a quarter of a mile of the granite. 



I had not time to follow it up. 



Considering the great development of trap in the Cossyah Hills, it 

 would seem remarkable that no sign of such a rock occurs in the section 

 across the same range in North Cachar. The fact is in accordance with 

 the view here adopted regarding the age of this rock; the whole 

 range is there formed by cretaceous and tertiary formations. I may also 

 notice that I did not meet with trappean rock anywhere in Assam, 

 unless as boulders in the great Himalayan torrents. 



In the two sections we have noticed at Mawbelurkar and Terria, 



trap has been seen as the chief underlying rock ; 

 Otlier subjacent rocks. i p i i • i t 



and from the tact that m one locality at least it is 



stratified, one might suppose tliat its underlying the other rocks 



E ( 119 ) 



