44 GRIMES: MY1NGYAN, MAGWE AND PAKOKKU DISTRICTS.^ 



is cut out and the pliocene sandstones are resting on still lower 

 Yenangyaung beds. This great difference in the thickness of the 

 miocene beds on the two sides of the anticline, and the change of 

 the miocene beds next to the boundary, show that it must either be 

 faulted or unconformable. That it is not faulted is, I think, evident 

 from the very steep, almost vertical, dip of both series, so that if the 

 differences in thickness of the miocene beds were due to faulting the 

 throw of the fault must be very great, and so much so as to be out of 

 the question. Another piece of evidence against a fault is the 

 occurrence, at one place, of the debris of the miocene in the basal 

 beds of the pliocene, so that there is an apparent transition between 

 the two. North of Seikkwa we see, at the top of the series, miocene 

 shales and sandstones, apparently somewhat broken up and frag- 

 mentary, passing down into ordinary miocene beds and upwards into 

 a whitish sandstone, containing miocene debris and pieces of 

 gypsum. This white sandstone contains fossil wood, and can only be 

 distinguished from ordinary Irrawaddi sandstone by the presence 

 of the pieces of gypsum, and it passes gradually into the typical 

 pliocene sandstone by the decrease of this gypsum. From these two 

 considerations we see that the boundary is not a faulted one, and so 

 between the miocene and pliocene there must be here a consider- 

 able unconformity. On the western side of the anticline this 

 unconformity is not very great, and the interval between the deposi- 

 tion of the miocene and pliocene beds was possibly of short duration. 

 On the east side of the anticline the beds show a much greater 

 unconformity, and the interval between miocene and pliocene was 

 probably greater, and there is one piece of evidence, which tends to 

 indicate that here the denudation of the miocene beds was still 

 proceeding, while the pliocene beds farther west were being 

 deposited, as on the western side of the Tangyi hills the basal 

 pliocene beds resemble those at Yenangyaung, and they have, inter- 

 stratified with them, the typical ^bands of ferruginous conglomerate, 

 which contain vertebrate remains ; but on the eastern side of these 

 ( 44 ) 



