16 THE COAL OF ASSAM. 



The point on which my season's work is most deticient is in the 



Further extension of examination of the important region south-west 



the Jaipoor field. f^.^^ Jaipoor, where, no doubt, the coal band is 



continued. Without official assistance, it would not have been safe or 



complications in the placement of the rocks of the latter region, the apparent sequence 

 being revcrsecU and that of the Jaipoor section being normal. It will not be easy to 

 make this matter intelligible to those who are not geological, but it is clearly part of the 

 practical question before us and must be attempted here. The general similarity of the 

 coal-bearing band in the two regions is quite sufficient to afford a prima facie proba- 

 bility of their identity, occurring, as they do, in such proximity and under physical 

 conditions so much alike. The coal seam at Jaipoor is, as I have said, associated with 

 the sandstone which overlies it. This sandstone is of marked Sub-Himalayan type (I 

 use this term with the more confidence as these rocks occur in every sense so character- 

 istically on the north of the valley), and is seen in the gorges of the Desang and of the 

 Dehing to pass upward through a great thickness of the same rock into such strata as 

 usually terminate that series, — clays, and coarse conglomerates. This must be a normal 

 section, fixing approximately the Jaipoor coal in the nummulitic horizon. In the Terap 

 and Namchik sections the sandstone alternating with the coal, and overlying it in consi. 

 derable thickness, is persistently of a markedly different kind from that at Jaipoor. 

 The alternative conclusions thus suggested are : — that the groups are different; or, that a 

 very considerable difference of condition affected the formation in the two regions j or, that 

 in the eastern sections the rocks ai-e inverted. This last supposition, which is the one I am 

 inclined to favor, also requires the suppression of a portion of the coal-rocks in each section: 

 I did not recognise the sandstone of the Terap measures at all in the Jaipoor section ; 

 but the base of this section is not exposed : the coal seam at the Terap is the lowest (or 

 hi'>-hest) bed seen; but it certainly is not at either limit of the coal band: in the Nam- 

 chik section, the supposition of partial suppression is also tenable ; and here we do find, 

 although the section is broken, strata of unmistakable Sub-Himalayan type in apparent 

 underlying sequence to the coal band. Thus it is seen that the supposition of inversion la 

 not gratuitous. There is, indeed, nothing in the nature of the rocks seen in the Namchik 

 sections, which need independently involve the reversion of the apparent order ; but the 

 normal ascending sequence of these Sub-Himalayan rocks is so well established, even, I 

 may say, in this neighbourhood, that the supposition becomes imperative of their being 

 younger than the rocks which here apparently overlie them. Still, inversion would not be 

 a necessity ; there might be a fault, or a compressed natural boundary between them, 



( 402 ) 



