An Outline of the Tertiary Geology of Burma. 485 



the east and west respectively.^ In several cases where it has been 

 examined the junction between the Tertiary and pre-Tertiary rocks 

 on the eastern side of the Arakan Yoma is faulted. It is quite 

 possible that a great line of dislocation exists between the two 

 — between the Arakan Yoma and its foot-hills — and if this were 

 the case the Tertiary region of Burma would in reality be a typical 

 rift valley. 



(4) Bordering the Arakan Yoma on the west is a strip of wild, 

 rugged ysountry, deeply intersected by bays and gulfs, and fringed 

 by islands forming the Arakan coast. It consists of Tertiary rocks, 

 which belong to the Assam Gulf of deposition as distinct from the 

 Burma or Pegu Gulf on the other side of the Arakan Yoma.^ 



III. The Geography op the Tertiary Period in Burma. 



No apology is tendered for attempting to consider the Tertiary 

 geology of Burma from the point of view afforded by a reconstruc- 

 tion of the geography of the period. The reconstruction is based, 

 of course, on detailed study in field and laboratory, a great part of 

 the information being now available in published form. Despite 

 the lack of knowledge concerning many parts of Burma, this palseo- 

 geographical picture may be considered as reasonably correct and 

 it helps to explaiii many facts otherwise difficult of interpretation. 

 More important, j^erhaps, it supplies a simple means of visualizing 

 and memoriziiag a mass of facts — an advantage not to be ignored in 

 attempting a comprehensive view of the world's stratigraphy. 



As already pointed out, the main folding of the Shan Plateau as 

 well as the earlier stages of the uprise of the Arakan Yoma took 

 place in pre-Tertiary, probably in late Cretaceous, times. There 

 is every reason to believe that the former was a land mass from 

 earliest Tertiary times and that the latter formed a narrow ridge 

 sej)arating two arms of the sea — the Gulfs of Assam and Burma. 

 The line of the Arakan Yoma is continued through the Andaman 

 and Nicobar Islands to Sumatra and Java, but most probably this 

 line was breached by the sea throughout the Tertiary period, just as 

 it is at the present day. The history of the Tertiary period in 

 Burma is largely that of the infilling of the Burmese Gulf — a great 

 geosyncline — by sediments both continental and marine. Flowing 

 into the gulf from the north there were one or more rivers which 

 poured in huge masses of sediment. The Irrawaddy of the present 

 day may be looked upon as the remnant of this great Tertiary 

 river-system (see Fig. 2). 



There has been, generally speaking, a gradual movement south- 



1 Cotter, " The Geotectonics of the Tertiary Irrawaddy Basin " : Joiirn. and 

 Proc. Asiatic Soc. Bengal, N.S., vol. xiv, 1918, pp. 409-20, especially p. 412 ; 

 Vredenburg, Eec. G.8.I., vol. li, pt. iii, 1921, p. 302. 



- Pascoe, " The Oil Fields of Burma " : Mem. O.S.I., vol. xli, pt. i, 1912, 

 pp. 179-99 ; Pascoe, " Oil Occurrences in Assam and Bengal " : Mem. G.S.I., 

 vol. xli, pt. ii, 1914. 



