186 AT TOUCHE: GEOLOGY OF NORTHERN SHAN STATES. 



teik gorge the base of the limestones is not visible, but at least 2,000 

 feet are exposed in the cliffs on the eastern side. 



A more complete section is exposed on the left bank of the 

 Nam Tu valley Nam-Tu to the north of Hsipaw, where the 



limestones occupy a band of about three 

 miles in width between the crest of the scarp of Silurian rocks 

 overhanging the river on the west and the red sandstones and 

 shales of the Namyau series to the east. Thus both the base and 

 top of the Plateau Limestones are well defined. The inclination of 

 the whole sequence is fairly uniform, and may be taken as 25 

 degrees on the average. This would imply a thickness of about 

 6,600 feet for the limestones ; but even here it is not certain that 

 some portion of them was not removed before the deposition of 

 { g . Q the overlying strata, for banks of calcareous 

 conglomerate filled with well rolled pebbles of 

 the limestone have been observed at several places at or near the 

 base of the Namyau beds, showing that some denudation had 

 taken place in the interval. 



The band of this limestone exposed on the northern flanks of 

 . j the Loi-len range, where the red beds are also 



in position above it, is fairly uniform in width 

 towards the western end of the range, and would measure about 

 5,500 feet in thickness, if we assume a dip of 45 degrees, which is 

 rather under than over the average amount. 



The prevailing type of the Plateau Limestone is a whitish or 



light grey rock, weathering to a darker grey 

 Litholoeical characters. , , i i r • i u .1 



and often stained red by iron oxide both on 



the surface and along the joint planes. It is often hard enough 

 to strike fire with the hammer, and when struck usually gives out 

 a more or less pronounced fetid odour, no doubt due to the 

 presence of decomposed organic matter. In texture it is sandy 

 to the touch and has a finely granular appearance, which at fiist 

 gives one the impression that it is a siliceous limestone ; but 

 examination of thin sections under the microscope and chemical 

 analyses show that the rock, except near its boundary with the 

 older formations, where it occasionally passes into a sandy lime- 

 stone, contains a very small proportion indeed of silica or argillaceous 

 matter. 



