UNCONFORMITY IN UPPER TERTIARY BEDS. 43 



given to this suggestion by the greater prevalance of gypsum in the 

 upper beds than in the lower. 



Between the upper miocene beds and the overlying pliocene 

 ' . t . ,. . (Irrawaddi) beds there is an unconformity, 



Unconformity between mio- v J J 



cene and pliocene. an( j \ n places a great thickness of miocene 



beds was removed before the pliocene sandstones were deposited 

 on them. The uppermost bed of the miocene series is a sandstone 

 of a brilliantly white colour, and this is seen in both the Yenangyaung 

 and Singu-Tangyi ranges of hills, in places 60 miles apart. Of this 

 bed a varying thickness is exposed all along the western side of the 

 anticline, but, with the exception of a few small patches south of 

 Singu, it is absent from the eastern. Even where it is continuously 

 exposed, there are signs that it has suffered somewhat from denudation 

 before the pliocene beds were deposited on it, as, when the boundary 

 is traced on the 8" = 1 mile maps, the surface of the white sandstone 

 is seen to be very irregular. On the west side of the anticline the dip 

 and strike of the adjoining miocene and pliocene beds are apparently 

 the same, but it is impossible to test this rigidly owing to the adjacent 

 rocks not having very definite bedding planes. On the eastern side 

 of the anticline we find that not only has the uppermost white 

 sandstone been denuded away, but several others of the upper 

 miocene beds also, and there is a great difference between the 

 thicknesses of the miocene beds on the opposite sides of the anticlinal 

 arch ; this difference gradually increases from the extreme southern 

 part of the miocene exposure, south of Singu, to a maximum at 

 Seikkwa (2 miles north of Yenangyat), whilst at Yenangyat we have 

 only 500 feet of miocene beds on the eastern side of the anticline, 

 and about 3,000 feet on the western side. The miocene and 

 pliocene beds on the east side of the anticline at Yenangyat also have 

 apparently the same dip and strike, but when mapping the Signal 

 hill sandstone I found that this is not so, and that the exposure 

 of it is not parallel with the boundary ; and besides, at one place, 

 for a distance of one and a quarter miles, the Signal hill standstone 



( 43 ) 



