80 NOETLING : PETROLEUM IN BURMA. 



formed by an alternation of thin, extremely regular beds £>f clay, and 

 somewhat thicker beds of sandstone, none of the layers exceeding 

 a few inches in thickness. These beds form an angle of n|° with 

 the beds of the lower sandstone (i). 



It is followed by a series, about 40 feet in thickness, of alternat- 

 ing beds of sandstone and clay, being again apparently horizontal; 

 it begins with a layer { sandstone (3), similar in appearance to bed 

 (1), which is followed by bands of very hard sandstone (4) and bluish 

 clay (5), each of which successively overlap the lower beds. 



This section proves in my opinion two points, viz. : 



{a) A contemporaneous erosion. 

 {b) A double unconformity. 1 



Another instance of contemporaneous erosion is illustrated in 

 figure 7, although it is here not so distinctly seen as in the former, 

 being affected by some features presently to be mentioned. 



It may be fairly supposed that within the petroliferous sands 

 similar features often occur. In fact, I believe,, that bed (1) in the 

 above diagram represents either the first or the second oil sand, and 

 that as a consequence their importance as a receptacle of the petro- 

 leum has been affected. On the other hand we see that under such 

 circumstances it is almost impossible to correlate the petroliferous 

 sands throughout the oil field, if we have no other feature to guide 

 us than the petroleum which they contain. 



(b) Veins of eruptive mud. — It is one of the strange features of the 

 Yenangyoung oil field, that although the strata were subject to fold- 

 ing, that this has not led to dislocations worth speaking of. There is, 

 of course, a certain amount of faulting, but the biggest throw which I 

 have observed amounts to less than 50 feet, and even this is not 

 quite clear. If any dislocations have taken place, they generally do 

 not exceed a few feet, and remain quite local. On the other hand 



1 The word unconformity is here used in a different and less significant sense than 

 is usual in English Manuals of Geology.— Ed. 



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