GENERAL GEOLOGICAL NOTES. 33 



■have not been traced, it is safer not to take this for granted, and to 

 adopt local provisional names. 



The abundance of silicified wood in the Tipam rocks, and its nature, 

 •suggest the question whether these rocks do not admit of correlation with 

 Mr. Theobald's ' fossil wood group ' of Pegu. Dr. Feistmantel examined 

 more than a dozen specimens of silicified wood, which I collected from 

 the former in different localities, and found them to be all exogenous and 

 of one species, apparently belonging to the order Asclepiadese, and similar 

 to wood brought by Mr. Theobald from Pegu. Mr. Theobald states 

 there is but one species of fossil exogenous wood in the province.* But 

 while he assigns a Pliocene age to the fossil wood group, the Nahuns are 

 considered to belong to the Miocene epoch. The former also would seem 

 to be in a somewhat less consolidated state than the Tipam rocks, and 

 beneath, intervening between them and the nummulitics, comes a very 

 important series of beds, called by Mr. Theobald the Pegu group. In 

 Assam, on the other hand, the Tipam strata rest directly on the coal- 

 measures, for which a nummulitic age has been suggested, although on 

 somewhat scanty evidence. Fossil wood occurs in the Dihing group as 

 well as in the Tipam, and the former is perhaps more nearly the repre- 

 sentative of the Burmese rocks, although the latter do not include con- 

 glomerates like those which form so marked a feature in the Dihing beds. 

 But different conditions of deposition are not unlikely. 



An important difference between the sections in the Dihing at 



Jaipur and at the Tirap quarries was pointed out 



Faulted boundaries. -^ , ^ ,^ i 



by Mr. Medlicott in 1865.t In the former the coal 



and associated shales are covered by the soft massive Tipam sandstones, 

 but in the neighbourhood of the Tirap they are overlaid by sandstones 

 of a markedly different type. The very cursory examination then prac- 

 ticable did not allow of Mr. Medlicott's arriving at a definite conclusion 

 as to the explanation of this want of uniformity. He pointed out that 

 the difference might be due to the coal rocks in the two localities being on 

 different horizons ; to the absence of strata in one which are represented 



* Vol. X, p. 252. t Vol- IV' ^^^^ P- 401- 



E ( 301 .) 



