2o8 M. H. LOVEMAN 



ARCHEAN SYSTEM 



The Mogok gneiss in this area is similar in every way to this 

 rock as described by Barrington Brown and J. W. Judd in the Ruby 

 Mines district and Coggin Brown in his traverse from Bhamo 

 in Burma to Teng-Yueh in Yunnan. Consequently the section 

 mapped here allows one definitely to connect those two areas. The 

 gneiss is present in a great variety of types and often assumes 

 both schistose and granitoid forms. All phases, from extremely 

 acidic to basic hornblende gneisses, are found. Bands of coarsely 

 crystalline limestone are present, as in the other areas of this rock. 

 In fact, this band of igneous and metamorphic rocks maintains 

 a great regularity in its diversity, whether examined far to the 

 south of Mandalay (east of Pyawbwe in latitude 20° 40') or in the 

 North at Teng-Yueh in latitude 25° 00'. Noteworthy at widely 

 separated points are the crystalline limestone beds. These 

 limestones are of considerable interest, first in that they house an 

 extremely varied collection of minerals, over twenty-five mineral 

 species having been identified by Barrington Brown and Professor 

 Judd, and secondly in that Professor Judd has argued in favor of 

 the inorganic origin of the limestone by means of the alteration of 

 the unstable scapolite contained in the basal gneisses. It would 

 appear that the practical continuity of this crystalline limestone, 

 in a well-defined zone more than two hundred and fifty miles in 

 length is almost conclusive evidence of its original organic origin. 



GRANITE 



The granite is discussed at this point because, although con- 

 siderably younger than the gneiss, being in fact intrusive into the 

 Cambrian sediments, it is always found either entirely within the 

 gneiss or along its eastern edges. On the map no attempt is made 

 to show the granite areas within the gneiss. There are, however, 

 no grounds for not beheving that the large mass of homogeneous 

 granite shown as occurring between the gneiss and the older sedi- 

 ments is not genetically the same as the very numerous bodies 

 of granite found entirely within the gneiss area. The granite is 

 a normal biotite granite and extremely consistent in its mineral 

 character over large areas; extreme variations occur, however, in 

 the texture from coarse-grained to fine-grained types. Intrusive 



