﻿642 ME. L. V. DALTOX ON THE [Nov. I908, 



(6) The increased thickness of the Pegu Group revealed by study of 



completer sections than those previously known. 



(7) The strongly-marked unconformity of the Irawadi Series to the Pegu 



Group as one recedes from the Irawadi, and the comparative 

 conformity in the less disturbed regions. 



It is suggested, as a point for further investigation, that there 

 appears to be a possibility of a small development of a coralline 

 fades in the Burmese Miocene (as in that of Java and India), 

 indicated by the fauna of the locality near Toungu (Thayetmyo 

 district), where a bed full of corals, including two genera new to 

 Burma, contains also two species of mollusks previously known 

 only from Java, and one new to science. 



Einally, the history of the Tertiary Era in Burma, as we now 

 know it, appears to have been much as follows : — In Eocene times, 

 a shallow sea seems to have extended from the base of the Shan 

 Plateau across the present site of the Arakan Yoma into India, 

 gradually deepening westwards, this being slowly filled up by 

 detritus of various kinds, until at the close of the period the 

 conditions led to the deposition of a thin bed of limestone over at 

 least the eastern area, after which some disturbance took place in 

 the west of Burma, as well as in the rest of Eurasia, whereby a low 

 ridge was formed along the line of the present Arakan Yoma, 

 constituting an imperfect barrier, higher and more effective in the 

 north than in the south. Thus, in Miocene times, a shallow sea 

 extended over the present Irawadi Valley, which received the 

 detritus of large rivers from the north and east. Deposits of 

 terrestrial vegetation were laid down near the land, giving rise to 

 coal-seams, while the sediments above and below were con- 

 glomeratic in their nature. At the same time that terrestrial 

 organic materials were being thus carried down, including bones of 

 land-animals, a marine and littoral fauna and flora existed in the 

 south, and in the more open portions to the north, giving rise by 

 their decay to petroleum-deposits. At length, the whole region 

 became estuarine, owing to the filling-up of the basin and to a move- 

 ment which greatly increased the height of the ' Arakan Yoma,' 

 •raising it above the sea, and led to the production of anticlinal 

 islands or shalloAvs in the sea to the east, while probably giving 

 rise to the Pegu Yoma. The result of this upheaval was the 

 denudation of the islands of partly- consolidated material, the 

 erosion being greatest in the most prominent: so that when, in 

 the Pliocene (?) Period, a thick series of estuarine and fluviatile 

 deposits was laid down over these, a considerable overlap resulted, 

 the Irawadi Series being quite conformable^ in places to the Miocene 

 below, and elsewhere resting across its upturned edges. Finally, 

 the whole region again became subject to a general elevation, 

 whereby the Irawadi Series was laid bare to denudation, and the 

 earlier anticlinal folds accentuated, resulting in the present con- 

 -formation of the land — the Miocene being once more revealed as 

 inliers in the mass of the Irawadi Beds, marking the position of the 

 islands in the earlier estuary. 



