SILURIAN SYSTEM : LOWER NAMHSIM STAGE. 



137 



if we follow up the section in the Lilu ravine, instead of ascend- 

 ing the spur. Here the variegated Naungkangyi shales are succeeded 

 normally, about a mile above the village, by the Orthis and Rafines- 

 quina beds of the lower Naungkangyis, with a higher easterly dip 

 than at Lilu itself. But a little further on, at the entrance to 

 a narrow gorge just above the small village of Napeng, we come 

 upon the sandstones, which were seen on the spur above, dipping at an 

 angle of 60° beneath the Naungkangyis. It seems then that what we 

 have here is in the first place an overlap by the Namhsim Sand- 

 stones of the Naungkangyis, subsequently dislocated by an over- 

 thrust fault or fold parallel to the river, the beds having given way 

 along the comparatively soft layers of the Naungkangyi shales, under 

 the stress of an impulse acting from the east, and been driven up 

 over the hard sandstone strata. The cause of such a dislocation 

 having taken place along this particular line is perhaps to be found 

 in the existence, only a short distance to the west, of the unyield- 

 ing mass of the older Chaung-Magyi rocks, forming the old land area 

 of Tawngpeng. The fault plane runs almost due north and south, 

 and has been traced from the Panghsa-pye saddle, where it passes a 

 short distance to the west of the village, into the Bawdwin area to the 

 north, beyond the limits of the map, where the disturbance of the 

 rocks caused by it has, no doubt, facilitated the impregnation of 

 the strata with the mineral ores for which that locality is famous. 



A short distance to the south of Panghsa-pye the fault dies out, 

 no definite signs of its presence having been 



Southern termination j , j ,1 • n <• ,1 -k T ' 



of the fault. detected on the south side of the Nam-sam 



valley. This fact is in accordance with the 

 supposition that (he locus of the fault was determined by the 

 presence of the old land area ; for on the latitude of Panghsa-pye 

 the bolder of this area changes its direction, and trends away to 

 the west, so that the 'anvil ' effect of this unyielding mass of rock 

 was not felt to the south of that neighbourhood. 



Several outliers of the Namhsim Sandstones occur on the eastern 

 side of the overthrust, on the spurs running 

 SutdataS ° f N " mhsim down t0 the western bank of the Nam-Tu, 

 forming conspicuous knolls or ridges, with 

 steeply scarped sides. The largest of these is on the Man-wing— 

 Man-ping spur,^ just above these villages (Plate 22) ; another is found 

 between Ngai-tao and Manglang on the next spur to the north ; 

 a third surrounds the village of Pangtawng, and a fourth occurs 



