An Outline of the Tertiary Geology of Burma. 495 



they do not appear to range higher. It will be noticed that at least 

 two of the foraminifera are Eocene forms. Taking a narrow 

 palaeontological view, one would be tempted to regard the Kyet-u- 

 bok Bed as Eocene. It is, however, distinctly a basal bed strati- 

 graphically and its characteristics agree very closely with other 

 typical basal beds. As a general rule, one may say that the fauna of 

 a basal bed of a formation comprises : — • 



(a) Survivors from the preceding stage which occur in enormous 

 numbers before their final extinction. Their number is frequently 

 increased by the presence of numerous rolled specimens. 



(6) Forerunners of the succeeding faunas. It is the presence of these 

 new elements in the fauna which should really decide its age. 



Amongst comparable examples may be noted the basal Ledian ^ 

 with its but slightly rolled Nuininulites Uevigatus (the zone fossil of 

 the preceding stage, the Lutetian) and the basal Ypresian, with its 

 numerous Landenian species ■,^ both examples being from the Anglo- 

 Franco-Belgian Basin. Amongst older rocks the basal bed of the 

 Devonian of the Welsh Borderland may be noted. ^ The Kyet-u- 

 bok Bed has been traced by the writer for a distance of about 35 miles 

 from near Ngajje to the south of Yenanma.^ It ajDpears to correspond 

 exactly to a bed found at the top of the Yaw Stage from latitude 

 20° 15' to 21° 15', characterized by the presence of Ortliophragmiyia, 

 Nummulites, Velates orientalis, Volutoconus hirmanicus, etc. 



Shwezetaw Stage. 

 In Lower Burma the lowest Pegu Beds are shales — forming the 

 lower part of the Sitsayan Shales of the Henzada and Prome districts. 

 Passing northwards to the neighbourliood of Yenanma and Ngape, 

 one fiiads the Basal Bed is succeeded by a series of shales and then 

 by a group of sandstones — the Shwezetaw Sandstones. The shales 

 are usually unfossiliferous, but the writer found an interesting fauna, 

 a few hundred feet above the base in Magyisan Chaung (latitude 

 19° 57'). The fossils have not yet been examined in detail, but they 

 include forms closely allied to, but specifically distinct from, species 

 described from higher horizons of the Pegu. Further north the sand- 

 stone facies invades the whole of the Shwezetaw Stage, and becomes 

 of shallower-water type. About latitude 21° the sandstones resting 

 on the fossiliferous Basal Bed contain coal seams, and the principal 

 fossil is the brackish- water Batissa (Cyrena). The more marine 

 type of Shwezetaw Sandstone (about latitude 20° 5'), seems to be 

 characterized by Ampullina birmanica Vred., and this fossil is also 

 found in the lowest Pegu (Shinmadaung Sandstones) where they rest 

 on pre-Cambrian in the Shinmadaung area. Interbedded igneous 

 rocks also occur in this district.® 



1 Stamp, Geol. Mag., Vol. LVIII, 1921, p. 198. 



^ Stamp, Proc. Geol. Assoc, vol. xxxii, 1921, pp. 97-8. 



3 Stamp, Abs. Proc. Geol. Soc, No. 1,075, 1921-2, p. 6. 



* It is almost certainly continuous with Cotter's G2 bed (op. cit., 1911-12^ 

 p. 226). 



* Vredenburg, Rec. G.S.I., vol. liii, pt. iv, 1921-2, pp. 359-69. 



