HISTORICAL SUMMARY. 



351 



and are either much attenuated, or absent, beneath the Plateau 

 Limestone further to the south, wherever the base of the latter is 

 exposed. The occasional presence of boulder conglomerates and 

 coarse grits at the base of this formation also indicates the proximity 

 of a coast ; and in one case at least, on the spur above Aunglok, 

 the boulders have all the appearance of shingle thrown up on a sea 

 beach. Further out to sea deposition seems to have taken place very 

 slowly at this time, and it is possible that some portion of the 

 marls that overlie the Llandovery graptolite band in the Eastern 

 Ranges were contemporaneous with the sandstones of the coast. 

 Towards the close of this stage the sea appears to have advanced 

 northwards again, for thin deposits of marl are found overlying the 

 sandstones, up to the edges of the plateau. 



The evidence as to whether any considerable disturbance of the 

 strata already deposited took place at the end 



Unconformity between f th Namhgim stage ig somewnat conflicting. 

 Silurian and Devonian. _ B . 



It is clear that in some places the 

 Nyaungbaw Limestones had been tilted and eroded before the 

 Zebingyi beds were laid down across their edges, but in other 

 places the sequence appears to be perfectly conformable. This 

 appearance of conformability, however, may be deceptive, for the 

 Namhsim sandstones are exposed almost invariably only along the 

 faces of precipitous scarps, and it is impossible to say whether they 

 had been tilted before the Plateau Limestones were laid down upon 

 them or not. It is pretty certain, however, that the latter were 

 accumulated in a gradually deepening and widening sea, for they 

 overlap everything beneath them ; and it seems quite possible that, 

 during the earlier stages of the movements that caused this depres- 

 sion, portions of the older sea-floor were raised above the water level 

 and exposed to denudation. The Zebingyi beds, which are extremely 

 local in development and variable in thickness, may have been 

 deposited in a lagoon or swamp bordering upon one of these 

 raised areas ; for they contain a good deal of carbonaceous as 

 well as calcareous matter, and have all the appearance of muds 

 accumulated in shallow basins of no great extent. 



The movements that ushered in the deposition of the Plateau 

 Limestone seem to have been of great im- 

 Easterly continuation por tance in the history of Gondwanaland, for 



of lndo-(iangetic deprcs- , . . * _ 



sion. they may have been the first symptoms, in 



the Indian region, of that break up of the old 

 continent which was destined, to modify so profoundly the distribu. 



