32 GEOLOGICAL NOTES ON ASSAM. 



without weight in the question of the age of these deposits^ for it is 

 at lesisi possible that the trap rocks here are related to some of the great 

 volcanic flows of India. This is the most positive addition I have to make 

 to our knowledge of the region; some of these trap rocks having heen 

 hitherto supposed to he more recent even than the nummulitic group. 

 The evidence is beyond doubt. Close to Mawbelurkar I obtained a 

 clear cliiF-section_, showing the altered and disturbed conglomerates to 

 be transversely overlaid by the conglomerates of the Cherra Series ; the 

 former belong to the Shillong group, the '^^ secondary sandstones" of 

 Mr. Oldham's description, and are seen to sin/c into the igneous rock, 

 upon which the younger conglomerates here rest undisturbed. 



The trap rocks have been observed in several positions, many miles 

 apart. It is probable that some of these will be found connected, even 

 at the surface, when the district is regularly surveyed ; and it will be 

 very interesting to trace their relationship, for they present very remark- 

 able differences. From the Kalapani Valley to beyond Sohiong, trap 

 occupies a great part of the section. It is, throughout, remarkably 

 uniform, — a dense, basic trap more or less highly crystalline, spheroidal 

 or sub-columnar. B-idges of several kinds of altered rocks are, as it 

 were buried in it, and are occasionally penetrated by veins from the 

 main mass. In the trap so extensively exposed 

 1 e J*ap> along the east flank of the Likenso outlier, at the 

 edo-e of the range, the characters are altogether diflerent. Here the 

 common varieties are vesicular, amygdaloidal, earthy, compact, excep- 

 tionally sub-crystalline. In places there is distinct stratiform structure ; 

 partino-s of earthy, almost shaly, rock separating thick masses of harder 

 varieties and assuming the general underlie in the region. I consider 

 these to be truly stratified traps. I looked as closely as my time 

 admitted for direct evidence of partial contemporaneity with the over- 

 lying sedimentary series, but unsuccessfully. The very marked pre- 

 valence in this position of dark green chloritic grains in the bottom beds of 



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