﻿Vol. 64.] GEOLOOr OF BUKMA. 621 



As to the thickness of the rocks included in the Pegu Stage, we 

 have data here to supplement the calculations published by 

 Dr. Noetling in 1901.^ First, there is the traverse of the shales 

 or clays intervening between the zones of Cytherea erycina and 

 Parallelipi^ediim ^prototortuosum, where these are exposed west of 

 Thayetmyo, which gives evidence of a thickness of not less than 

 1700 feet, bringing up the thickness of the beds between the zone 

 of Cytherea erycina and the top of the Pegu Group to 3200 feet, 

 assuming the thickness of the beds between the ' Kama Clay ' and 

 the top of the Miocene as 1000 feet. Secondly, there is the traverse 

 of the lower portion of the Pegu Group in the north-west of the 

 Thayetmyo district, where, assuming the fossils found near the 

 crest of the Mindegyi anticline to represent an horizon approxi- 

 mately equivalent to the zone of Cytherea erycina (and the zone of 

 Cantharus Martinianus must be considered as such), we obtain a 

 thickness of not less than 4500 feet for the beds between the 

 nummulitic limestone at the top of the Eocene and the zone of 

 Cytherea erycina, or a total thickness for the Pegu Stage of about 

 7500 feet. This is under, rather than above, the actual amount 

 where the series is fully developed, although the varying uncon- 

 formity of Miocene to Pliocene prevents anything like accurate 

 determination. 



The Irawadi Series needs further detailed examination before 

 more than general views can be expressed with regard to it. The 

 similarity of the deposits to those of the Siwalik Beds of India 

 leaves little doubt that they are at least approximately contem- 

 poraneous with them, and therefore, according to the view adopted 

 by the majority of authors, of Pliocene age. This opinion, it may 

 be said, entirely accords with the great contrast observed between 

 the characters of the sediments of the Arakan and the Irawadi 

 Series, with the unconformity of one to the other, and with the 

 homogeneity of the thick mass of incompact sands that constitute 

 the highest-seen Tertiary beds of Burma. 



We arrive, then, at the following revised arrangement of the rocks 

 of the west of Burma, which is, as far as possible, in accordance with 

 the latest knowledge : — 



Thickness 

 in feet. Age. 



Ieawadi Series 20,6oO(?) Pliocene(?) 



Arakan Series I ^®8'^^''°"P ^^^^^ Miocene. 



ARAKAN bERIES I g^ggg.^(^^^^p g^^^ Eoceiie. 



( ( Cardiia-'BediS, (?) Cretaceous. 



A Q J Upper. -^ jSaZoSm-Limestones (?) Triassic. 



AXIAL SERIES ^ [ Shales, schists, and grits . (?) (?) 



Lower. Flaggy shales and schists. (?) (?) 



^ Palasontologia Indica (Mem. Geol. Surv. India) n. s. vol. i, no. 3, p. 26. 



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