YENANGYOUNG. 87 



hb. The longitudinal arch.—\ understand under this term the 

 low arch which is formed by the strata in the direction of the 

 axis of the anticlinal. As already stated, its presence was first 

 discovered after mapping the Yenangyoung oil field ; the presence 

 of such a dome shaped anticlinal was made apparent only after 

 mapping the outcrop of the zone of Hippotherium antelopinum. 



This zone forms a well marked horizon in the sequence of the 

 strata, and crops out in the shape of an elongated ellipse, the long 

 axis of which measures two and a quarter miles, while the short 

 (transverse) axis amounts to slightly over a mile only. 



It was desirable that the view thus theoretically obtained should 

 be confirmed by actual observations, if possible. It is of course 

 obvious that observations of this kind require the greatest care, — in 

 fact to be of any value, they could be only carried out strictly along 

 the axis of the anticline ; but even then it will be seen that, 

 from what I have said above with regard to local unconformities 

 and the inconstancy of the beds in horizontal direction (see page 78), 

 the possibilities are that the natural dip of the longitudinal arch 

 may be obscured by these features, and at any rate great difficulties 

 were to be expected in ascertaining facts with regard to its exist- 

 ence. 



However, I carefully examined the Yenangyoung oil tract, specially 

 with regard to the longitudinal arch, and the following are the 

 observations which I have made. South of Berne, particularly 

 along the Maung Aung Gyaw The-Yo, and to the north of well No. I, 

 the beds exhibit a distinctly southerly dip along the longitudinal axis 

 of the anticline, which, however, and this is the remarkable part 

 of it, seems to be limited to a certain restricted area, north, south and 

 west of which the strata exhibit their regular western dip. In this 

 case it is not quite certain whether this southern dip is not due to a 

 local sliding of at least a part of the upper beds on the soft clay 

 below ; it may also be that the southern dip indicates the presence of 

 another structure presently described as intersecting folds. The 

 ground however was not favourable for further examinations, neither 



( '33 ) 



