40 GRIMES : MMNGYAN, MAGWE AND PAKOKKU DISTRICTS. 



quite common to see sandstones changing into* shales, or vice versd 

 within a short distance. Dr. Noetling, in his Memoir, 1 has divided up 

 the bottom 500 feet of these beds, which are exposed on the eastern 

 side of the anticline at Yenangyat, but an examination of the country 

 to the north and south of this place shows that, owing to the rapid 

 changes in the beds, this subdivision only holds good for the immediate 

 neighbourhood of Yenangyat. Many of the beds, however, are very 

 persistent, and one of the sandstones, which w r as named Signal hill 

 sandstone by Dr. Noetling, I have mapped in order to show the 

 structure of the country better ; this at Yenangyat is a soft yellowish- 

 brown sandstone, which, when traced along its outcrop, shows very 

 great alterations, both in character, varying from fine-grained rock 

 to conglomerate, and thickness, sometimes almost dying out and at 

 other times 30 or 40 feet thick. 



The uppermost bed of the upper miocene is, however, when 

 present, quite distinct from the beds below, and it can be easily identi- 

 fied, especially as its colour is so conspicuous, that it can often be 

 distinguished at a considerable distance off. In the southern part 

 of the Yenangyaung oil-field it is a very soft sand-rock of a brilliant 

 white colour, sometimes tinged with blue, red, etc., and it is in striking 

 contrast to the dull yellowish-brown sandstones below it. It usually 

 contains pieces of gypsum, and in a few places, fragments of wood 

 partly replaced by oxide of iron, etc., these last are very friable and 

 so quite unlike the fossil wood in the Pliocene beds above. This 

 upper sand is of very variable thickness ; it is exposed all along the 

 western miocene boundary on the Singu-Yenangyat anticlinal arch, 

 but, with the exception of a small length at the southern end, it is 

 not present on the eastern side. 



The thickness of the upper miocene beds varies, I believe, very 

 considerably, but this I was unable to thoroughly test owing to the 

 limited area of my maps, as only at one place — 3 miles south of 



1 Memoirs, G. S. I., Vol. XXVII, Part 2, p. 127. 

 ( 40 ) 



