An Outline of the Tertiary Geology of Burma. 487 



An extreme case, and one of great interest, of the effect of the minor 

 folding in the floor of the geosyncHne is seen around Shinmadaung 

 near Pakokku.^ Here, in the very midst of the Tertiary Belt, a ridge 

 of the pre-Cambrian gneisses, which must evidently form the floor 

 of the old gulf, appears at the surface as a result of folding and 

 faulting. The exact relationship with the surrounding Pegu rocks 

 is uncertain, but the lowest Pegu (Shwezetaw Sandstones) appear to 

 rest directly on the gneiss. It may be noted that this locality is 

 along the line of Tertiary volcanoes which passes through the midst 

 of the Tertiary Belt. Around Shinmadaung igneous rocks are found 

 interbedded with Pegu and probably with Irrawadian sediments. 



IV. The Tertiary Succession and its Classification. 



From what has already been said it follows that the Tertiary 

 succession in Lower Burma is very different from that in Upper 

 Burma. A failure to recognize the imi^ortance of lateral variation 

 and the wedging out of marine beds when followed northwards has 

 caused considerable confusion and invalidates much that has been 

 written on the Tertiary geology of Burma. The progress which has 

 been made in this respect within the last few years is largely due to 

 the work of Dr. G. de P. Cotter. 



It may be said at once — 



(a) that very little is known of the succession in the Sittang Valley, 



that is to say, on the eastern side of the Pegu Yoma, 

 {h) that the Eocene strata are very imperfectly known, 

 (c) that many points in the correlation of the succession in Upper and 



Lower Burma are still uncertain. 



It is found, however, that most of the principles of the cycle of 

 sedimentation can be applied on a large scale to the interpretation 

 of the Burmese sequence. An attempt has been made to express 

 the classification and correlation in the form of a diagram (Fig. 3). 

 The diagiam also indicates roughly the lithology of the beds. Under 

 " continental " are included aeolian, lacustrine, fluviatile, and some 

 brackish water deposits. ^ 



Eocene. 

 1. Southern Region (Nicobar and Andaman Islands and Lower 



Burma). 

 In the Andaman Islands ^ the Eocene is represented by a series 

 of conglomerates and sandstones resting unconformably on, and 

 containing pebbles derived from, the underlying rocks, which are 

 probably Cretaceous and comparable with the Axial Group of the 

 Arakan Yoma. In passing it may be noted that the deepest water 

 in Eocene times lay to the south and the deposits of this age are 

 represented by limestones in parts of Sumatra and Java. 



1 Vredenburg, Rec. G.S.I. , vol. liii, 1921 (1922), p. 365. 



^ Most of the places mentioned in the following account will be found on the 

 maps, figs. 4 and 5. 



•'' Tipper, " The Geology of the Andaman Islands with references to the 

 Nicobars " : Mem. G.S.I., vol. xxxv, pt. iv, 1911. 



