352 LA TOUCHE : GEOLOGY OF NORTHERN SHAN STATES. 



tion of sea and land in the southern hemisphere in more recent 

 times. If we look at a geological map of India and Burma, we see 

 that the portion of the Shan States that we are now dealing with is 

 in a direct line with the great depression that extends from W.N.W. 

 to E.S.E. across the northern end of the Indian Peninsula, from the 

 Indus, at the point where it breaks through the Salt Range in the 

 Punjab, to the southern flanks of the Assam Range. If we produce 

 this line, which corresponds with the direction of the Himalayan 

 ' foredeep ' (Vor-tiefe)i across the Chin-Lushai Hills and Upper 

 Burma, which are entirely occupied by deposits of Tertiary and Recent 

 age, we find that it meets the western scarp of the Shan plateau 

 at the only point where the Plateau Limestone breaks through the 

 barrier of Archaean rocks, which otherwise extends in an unbroken 

 belt from the head of the Irrawaddy north of Bhamo to the sea at 

 Moulmein. Moreover, the manner in which the Plateau Limestone 

 disappears beneath the alluvium of the Irrawaddy is no less significant. 

 There is no diminution of the thickness of this formation as it 

 approaches the plains, but layer after layer of massive limestone 

 plunges out of sight until we reach the highest beds of the series, 

 with Fusulina, at Tonbo. It is evident, therefore, that the full 

 thickness of the formation is present here, and that its actual 

 westerly limit does not mark the original edge of the basin in 

 which it was accumulated. 



Immediately in front of the scarp, however, in the plains inter- 

 vening between it and the Irrawaddy and on 

 Archaean rocks in Ir- the western bank of that river, we 'find that 



rawaddy valley. 



the only rocks protruding from the alluvium 

 are portions of the Archaean floor, among which there is no trace of 

 Palaeozoic rocks, and this fact seems at first sight a serious obstacle 

 to the supposition that the Carboniferous sea was prolonged west- 

 wards. 



But it is to be observed that these ancient rocks were brought 

 to the surface in upper Tertiary times, since 

 Origin <>f western Qn the western side they are in continuous 



scarps ol plateau. . J 



contact with sandstones of that age. In fact, 

 it is evident that the whole length of the western edge of the 

 Shan plateau is a fault scarp, due to a great fault which, in the 

 portion we are dealing with, is duplicated, one branch following 

 the edge of the alluvium east of the Irrawaddy, while the other 



l Das Antlitz der Erde, Vol. Ill, Pt. 2, pp. 3;$5, 581. 



