TAWNG-PENG SYSTEM : CHAUNG-MAGYI SERIES. 



53 



taking the stratigraphical evidence alone into consideration, the 

 Chaung-Magyi rocks should be considered as pre-Cambrian. So far, 

 however, as the lithological evidence goes there is no reason 

 why they should not be placed in the lowest division of the 

 Cambrian system, for they show very slight traces of alteration, the 

 so-called quartzites being often indistinguishing under the microscope 

 from ordinary sandstones, while in only a few instances has a 

 secondary growth of the quartz grains been detected. The drawn 

 . out patches of ferruginous matter referred to 



° 'on page 48 as characteristic of the slates and 



probably representing granules of oxidised pyrites are practically 

 the only signs of alteration that these beds show, and I would 

 not have been surprised at any time to find traces of organisms 

 in them. I have, however, searched carefully through many out- 

 crops, especially of the black carbonaceous shale which occurs in 

 places, without discovering any sign of a fossil. 



I have been much struck with the resemblance between these beds 

 and those of the Shillong series in the Khasi 



ShiUongsS". With Hills of Assam - Both series are made U P of 

 slaty shales and quartzites, and the soft, sandy 



character of the latter rocks in the Khasi Hills, especially in weather- 

 ed outcrops, is identical with that of the Chaung-Magyi quartzites. 

 The series resemble each other also in containing no trace what- 

 ever of interbedded limestones. 



The Shillong quartzites and slates have been conjecturally cor- 

 related, both by Sir T. Holland 1 and Mr. 

 Dhamaradoubtful. ^ Vredenburg, 2 with the Dharwar system of 

 Southern India, but their similarity with the 

 Chaung-Magyi rocks leads me to think that they are perhaps of 

 not so great an antiquity. It seems to me much more probable 

 that the crystalline limestones, with the associated pyroxene and 

 scapolite gneisses and granulites of the Ruby Mines represent the 

 Dharwar system in this area, and that, like the Dharwars of the 

 Indian peninsula, they will be found to be folded in among the 

 biotite gneisses along definite lines. If this is the case, the Chaung- 

 Magyi rocks, the alteration of which is absolutely nil in comparison 

 with that of the highly metamorphosed crystallines of the Ruby Mines 

 area, must be much younger in age. They would correspond then 



1 Sketch of the Mineral Resources of India, p. 2. 



2 A Summary of the Geology of India, Calcutta, 1907, p. 16. 



