An Outline of the Tertiary Geology of Burma. 497 



0. digitata, and 0. gingensis. It is doubtful whether this stage is 

 really separable from the Pyalo Stage. 



Summarizing, it m.ay be said that, independently of tlieir exact 

 age, the higher beds ot" the Pegu (as at Minbu, Yenangyaung, and 

 Yenangyat) are characterized by the presence of large CyrencB — 

 C. {Batissa) crawfurdi, C. (B.) noetlingi, C. (B.) jyelrolei, etc> These 

 fossils occur also in the basal Irrawadian, probably derived. 

 Throughout the Pegu there is a marked increase in shallow-water 

 characters northwards. ^ The more homogeneous clays and shales 

 of the south give place to the alternating shales and sandstones of 

 the great oilfields. At Singu conglomeratic bands and " Bone 

 Beds " are frequent, whilst further north remains of crocodiles and 

 land vertebrates are found and lateritic " Red Beds " appear. 



2. The Continental Post-Eocene or Irrawadian System and " Fresh- 

 water Pegu ". 



The '■' Freshwater Pegu " is naturally restricted to the more 

 northerly parts of Upper Burma. North of latitude 21° 30' the 

 Eocene Yaw Stage passes up gradually into a mass of somewhat 

 coarse sandstone. At the base, logs of wood bored by molluscs and 

 afterwards silicified are frequent, whilst in the higher part, and 

 especially further north, silicified wood is abundant. North of 

 latitude 22° 45' the Freshwater Pegu rests directly on the Pondaung 

 Sandstone, and bands of quartz-pebble conglomerate and lateritic 

 " Red Beds " become frequent. Vertebrate remains— especially 

 crocodilian — are occasionally found, and the occurrence of Cadur- 

 cotheriimi in the higher beds near Myaing has already been mentioned 

 (in the relative position marked " f " on Fig. 3). 



The Irrawadian of Upper Burma comprises a thick series — 

 certainly more than 5,000 feet in the neighbourhood of Yenangyaung 

 — consisting mainly of coarse, current-bedded sands. At the base 

 there is usually a well-marked " Red Bed " or old lateritic land 

 surface. Associated with this band either above it or below, there is 

 frequently a bed of white sand rich in kaolin. Interbedded bands 

 or even beds of some thickness of a clay, which approaches pipe- 

 clay in general characters, are frequent in the lower beds and again 

 in the higher part of the Irrawadian. The Irrawadian is famous 

 for the enormous quantity of silicified fossil wood which it contains — 

 hence the old name " Fossil Wood Group " (Theobald). The series 

 has also yielded a number of interesting vertebrate remains, 

 notably near Yenangyaung. Specimens from this locality come 

 from two distinct horizons : — 



(a) Lowest beds containing Hipparion ptinjabiense Lyd. (Hippotherium 

 antilopinum of Noetling and earlier wTiters), Aceratherium lydekkeri Pilg. 



1 Pascoe, Rec. G.S.I., vol. xxxvii, pt. iii, 1908, pp. 143-6, but see Vredenburg, 

 ibid., vol. li, pt. iii, 1921, pp. 262-6. 



2 Cotter, Rec. G.S.I. , vol. xxxvii, pt. iii, 1908, pp. 149-55 (Taungtha Hills) ; 

 €otter, ibid., vol. xxxviii, pt. iv, 1909-10, pp. 302-7 (Yenangyat). 



VOL.LIX. — NO. XI. 32 



