GEOLOGY. 133 



them arc broad bands of fine-grained unstratified argillites of the 

 Mergni Series, with an incipient cleavage parallel to the general 

 strike. 



Usually these agglomerates or greywaokea form wide bars across 

 the streams, with cascades and rapids, and the higher ridges are 

 made up of them, owing to their superior resistance to denudation 

 as compared with the argillites. 



Impure sandstone quartzites are met with, but not commonly, 

 as a sandy modification of the argillites and 

 ar zl es interbedded with them. A broad zone of purer 



quartzites crosses the Tavoy river above and below Shintabi and 

 is excellently exposed on the road between Shintabi and Pachaung. 

 They are fine-grained, unstratified rocks with irregular and shattery 

 jointing, showing under the microscope a mosaic of quartz clouded 

 with aluminous material, and arc traversed by veinlets of finer 

 quartz. Their clastic origin is obscured by subsequent changes, 

 and, as is usual in fairly pure sandstones, metamorphism has been 

 much more effective than in the associated clay rocks. 



Although they do not rise to great heights they form bold and 

 rugged ridges and the picturesque gorge of the Tavoy river between 

 Kyaukshat and Sanchi is cut through them. Above and below 

 the narrows, where the river passes over more easily eroded argil- 

 lites, the valley opens out to a broad " strath." 



Apart from the agglomerates, true conglomerates appear to be 



very rare. A coarse conglomerate, with well 



Conglomerates. rounded pe bbles, is recorded from near 



Pachaung, but neither of the authors has seen it in situ. 



Thin-bedded and usually impure limestones of blackish or 



red colour, though sometimes crystalline, have 



Limestones. been geen at various i oca lities in river beds, 



with field relationships to the Merguis leaving little doubt that 

 they form part of them, as for example, between Yapu and Migyaung- 

 laung on the Tavoy river, several points on the Ban and its tribu- 

 taries and near the Siam frontier. 



The outcrops on the Tavoy river, of which there are five, are 

 flat expanses projecting a foot or two above the lowest water- 

 level. The limestone is both massive and in thin shaly beds which 

 dip to south-west and west-south-west at 40°. There are two 

 varieties, one fine-grained, homogeneous and unaltered, though much 

 shattered, the other white and saccharoidal, full of irregular knots 



