86 NOETLING : PETROLEUM IN BURMA. 



The anticlinal and dome-like structure.— The late Dr. Oldham, 

 when visiting Yenangyoung in 1855 had already noticed that the oil 

 fields were situated on the crest of an anticlinal flexure ; he simply 

 mentions the fact, without any further theorizing. In 1888 I was able 

 to fully confirm Dr. Oldham's observations and to give some details 

 with regard to the structure of the anticlinal arch. After the topo- 

 graphical survey had given the basis for a trustworthy geological map, 

 a new structural feature was discovered. The peculiar mode of 

 outcrop' of the zone of Hippotherium antelopinum y proved that it 

 was not only a simple anticlinal arch, but that the general struc- 

 ture of the Yenangyoung oil field was that of a low dome or " turtle- 

 back " fold. 



aa* The anticlinal arch, — The anticlinal arch formed by the 

 tertiary strata at Yenangyoung is comparatively flat and broad, in 

 consequence of the low angle of dip of the strata ; nowhere does 

 this exceed 40 , and even such a high angle has only once been 

 noticed on the eastern side of the anticline. The angle of dip de- 

 creases towards the centre of the anticline. In passing over the 

 arch from west towards east we see the angle of dip of 37 to 38 

 on the bank of the river gradually becoming flatter till the axis of 

 the anticline is reached, where the strata appear horizontal for a short 

 distance ; after which the angle of dip again gradually increases till it 

 reaches its maximum of 39 to 40 , which it keeps on as far as I have 

 examined the country. 



The anticlinal arch appears therefore almost symmetrical, but it is 

 quite certain that it dips slightly steeper towards the eastern side. 

 The direction of dip is very regular and generally south-west on 

 the western and north-east on the eastern side. It varies slightly 

 of course, and its magnetic bearing may be said to oscillate be- 

 tween 6o° to 68° west of south or east of north. 



Necessarily the direction of the strike varies also, and its direc- 

 tion ranges from 325 to 330, but within this range it keeps the 

 direction very steadily. 

 ( *32 ) 



