GEOLOGICAL NOTES ON ASSAM. 49 



The north-easterly extension of the Bun-ail is the Patkai range of 



Upper Assam. I have only seen the very outer 

 Patkai range. ri i 



flanks of this on the skirts of the valley. In 



this position two groups of rocks can be roughly indicated — a great 

 thickness of characteristic Sub-Himalayan strata^ and the rocks associat- 

 ed with and forming the coal measures. The latter have been con- 

 jecturally identified as nummulitic upon the evidence of their close 

 conformable relation to the lower Sub-Himalayan rocks, supported by 

 the known occurrence of coal of this age in the Cossyah Hills. The 

 direct. resemblance between the groups at the two localities is not marked. 

 The coal-sandstone at the Terap is a fair representative of the rock at 

 Cherra_, but shales predominate in the Assam measures, and the coal- 

 seams are numerous and regular. It is by no means unlikely that some 

 of the sandstones below the coal are cretaceous. In the preceding coal- 

 report I have given some detailed observations of the sections in these 

 regions. I need here only mention that the rocks are everywhere 

 greatly disturbed, and that the almost universal underlie is southerly 

 towards the Patkai ridge. 



From the information I received from Captain Godwin Austen 

 just before starting for Assam, that on parts of 



Sub-Himalaya. i -r.i , 



the Jihootan frontier the crystallme rocks came 



to the edge of the plains, I was quite prepared to find Sub-Himalayan 



rocks wanting throughout Assam. I was therefore somewhat surprised 



to find them in full force throughout all the upper part of the valley. 



In the gorges of the hills north of Tezpoor and Dibroogurh one could 



not tell them from the Sivaliks of the North-West Himalaya — immensely 



thick strata of light grey sandstones, having a constant dip towards the 



main hills to the north. I could not penetrate any distance in these 



hills to see the extent of these rocks or their relation to those inside 



them. The really wild men, Akahs, Duphlas, Abors, ]\Iishmies, &c., who 



inhabit these inaccessible ridges, are veiy much opposed to visitors, and 



G ( 435 ) 



