128 NOETLING: PETROLEUM IN BURMA. 



the Yenangyoung stage cannot be less than 500 feet, and the chief 

 subdivisions seem to form fairly constant horizons as may be seen 

 along the eastern slope of the range (see PI. XVII). 



(b) The lower Miocene beds or Prome stage, 



Lithological characters. — They are the same as already described 

 greyish glauconitic sands alternate with bluish, rather tenacious clays. 



Palceontological characters. — The uppermost bed of the Prome 

 stage, a very glauconitic sand, which therefore appears dark green, 

 has yielded a very interesting fauna, which I described in part I 

 of this volume of the memoirs. It is unnecessary to repeat here 

 the list of fossils. It is sufficient to say that they furnish evidence of 

 an unmistakably miocene age of the beds in which they are contain- 

 ed and that their character is purely marine. 



Local sub ^division .— -The boundary between the Prome and 

 the Yenangyoung stages is less well defined at Yenangyat than at 

 Yenangyoung. In fact it may be questioned whether the sub- 

 division of the miocene beds answers the natural conditions best. I 

 have laid the boundary between the Prome and Yenangyoung stages 

 above the first oil sand, but below the thick bed of olive coloured clay 

 No. 9, thus separating the beds characterised by abundance of gypsum 

 in the argillaceous beds from those without gypsum, the arenaceous 

 beds of which generally contain petroleum. As already stated, this 

 subdivision may perhaps be an artificial one, and it would perhaps be 

 better to consider the whole sequence of beds below the Irawacli series 

 as belonging to one and the same series, but it must be borne in mind 

 that the term "Yenangyoung stage" represents only the upper mio- 

 cene beds which, owing to some characters, chiefly the colour of their 

 sandy beds differ from the lower strata. The Prome stage, as defined, 

 is almost solely known from the deep borings, the insignificant 

 outcrop of the topmost oil sand being too badly exposed to be of any 



value. 



So far it seems that any general subdivision is impossible. The 

 wells have revealed a sequence of arenaceous and argillaceous beds 

 alternating and succeeding each other, but whether these can be con- 



_ ( *74 ) 



