184 LATOUCHE: GEOLOGY OF .NORTHERN SHAN STATES. 



These limestones extend northwards on the eastern side of the 



„ , . Nam-Tu beyond the limits of the map, but 



lyorthern extension. . . , 



how tar is not yet known, Similar lime- 

 stones have been found in Yunnan, and the expeditions of Rich- 

 thofen, Loczy, and others have shown that rocks of the same age 

 are spread over a wide area in China, but how far these correspond 

 with their development in the Shan States 

 cannot yet be determined. They also extend 

 eastwards across the Salween river into Kengtung, probably as far 

 as the Mekhong and the frontier of Siam, but nothing further is yet 



known of the geology of the Trans-Salween 

 Western limits. n .t i i- 



country. On the west the limestones come 



down for a short distance, opposite Mandalay, to the edge of the 



Irrawaddy alluvium, as the map shows ; but to the north and south 



of this interval they are separated from the plains by a strip, of 



varying width, of crystalline Archaean rocks. 



Whether the Plateau Limestone once extended much beyond its 



T . „ „ t present limits in the Northern Shan States. 



former extent <>1 £ . 



formation. and has since been removed by denudation, 



it is difficult to say. Facing the Irrawaddy valley on the west, and along 

 the line dividing the plateau from the hilly country of Tawngpeng 

 to the north, the edge of the plateau is usually a precipitous scarp, 

 evidently the result of long continued sub-aerial denudation, sej ara- 

 ted from the more rugged country beyond by a more or less broad 

 valley, on the floor of which the rocks below are exposed. But no 

 outlying masses of the limestone have been found resting on the older 

 locks beyond the valleys, and there is nothing to show that it ever 

 extended further than the base of the hills. At other places, where 

 no stream runs along the base of the older hills, as for instance on the 

 flanks of Loi Ling and the Loi Pan - Loi Twang range, the undulating 

 plateau continues uninterruptedly up to the very foot of the high 

 ground, giving the impression of a group of mountainous islands rising 

 from an encircling sea. But this appearance is to a certain extent 

 deceptive, for in some instances, as in the Loi-len range, the lime- 

 stones arch over the older formations, and in others a fringe composed 

 of the formations lying between the ( haung-Magyi series and the 

 Plateau Limestone intervenes, showing that the disturbances which 

 led to the upheaval of the higher ranges to their present relative 

 altitude took place since the deposition of the limestone. It seems, 

 however, quite possible that, while the limestones were being 



