TAWNG-PEXG SYSTEM : INTRUSIVE ROCKS. 



59 



ancient land. Under such circumstances it would be quite natural 

 that the volcanic deposits would be partly removed by denudation, 

 either marine or sub-aerial, and partly overlapped and concealed 

 by the succeeding strata, so soon as the conditions became favour- 

 able for the deposition of the latter. It may be conjectured, there- 

 fore, that the volcanic rocks belong neither to the period of de- 

 position of the Chaung-Magyi series nor to that of the succeeding 

 formations, but occupy an intermediate position. As they partici- 

 pated in the disturbances that affected the Chaung-Magyi series, 

 and are not fossiliferous, but formed a portion of the rocky floor 

 on which the succeeding formations, the age of which can be de- 

 termined by fossils, were laid down, I prefer to classify them for 

 the present with the older rocks. 



Intrusive Rocks. 



Among the Chaung-Magyi rocks great intrusions of granite are 

 found in some places, especially in the main 



Intrusive granite. m „ , . , ■, , 



area in Tawng Peng, which may perhaps be- 

 long to the same period as that in which the ejection of the rhyo- 

 lites took place. These rocks are especially conspicuous in the 

 neighbourhood of Nam Hsan (E 1), the capital of the Tawng Peng 

 State, which is built upon them near their eastern edge, and where 

 they occupy a large area, extending for several miles to the south, 

 west, and north. Large dykes of granite also proceed from this 

 granitic expanse towards the north-east, to within a few miles of 

 the rhyolitic area of Bawdwin. Intrusions of granite also occur 

 among the Chaung-Magyi rocks on the north side of Loi Pan, in 

 Mong Tung State, and along the southern slopes of Loi Ling in 

 South Hsenwi. 



The rock is an ordinary granite, consisting of quartz, orthoclase, 



felspar, sometimes microcline, and biotite, and 

 ^Petrographical char- ^ evidence of intenge curshing . 



The felspar in a mass of granite, capping a 

 hill at Loihkam (D 1), 21 miles west from Nam Hsan, consists 

 almost entirely of microcline. It differs from the granite of the 

 Kuby Mines district, described above, in containing no tourmaline. 

 It is somewhat remarkable that instances of the intrusion of 

 basic rocks are exceedingly rare in that part 

 Intrusions of basic 0 f the Shan States described in the present 

 rocks - Memoir. Throughout the whole ol the periods 



