ANCIENT SCHISTS, INDOCHINA. 23 



Alps of eastern Tibet. He describes the rocks as monotonous clayey 

 sandstone, of gray and dark colors, associated with clay schists and also 

 with amphibolite and chlorite schists. The presence of the latter leads 

 him to correlate the series with the Wu-t'ai. Semicrystalline limestones 

 occur beneath the sandstones, the strata being extensively intruded by 

 granite. 



Throughout much of Indo-China there occur ancient schists which are 

 described by Fuchs and Saladin,* who distinguish two varieties, the one 

 greenish, siliceous, hard, and compact, apparently the upper part of the 

 terrane; and the other a gray, lustrous schist. These metamorphic rocks 

 are associated with granite, which, as we may infer from the language of 

 the authors, is probably intrusive. The petrographic description is suf- 

 ficiently close to that of Loczy to suggest that these metamorphic strata 

 correspond with the supposed Nan-shan sandstone occurring between the 

 Ta-tsien-lu and Ba-t'ang, especially as the mountain ranges and structural 

 features are continuous. The schists are, however, classed by Fuchs and 

 Saladin as possibly Silurian (probably in the sense of early Paleozoic) as 

 they underlie fossiliferous Devonian schists and sandstones; but the strati- 

 graphic relations have not been worked out and it is not clear how old the 

 pre-Devonian rocks may be. In a recent letter from M. Emm. de Mar- 

 gerie my attention is called to the occurrence of extensive and massive 

 conglomerates which may represent the lower Cambrian or pre-Cambrian 

 glacial deposits in this region. 



Westward from Yiin-nan and Burmah in the Himalayas occur ancient 

 rocks which were described as an older granite-gneiss and a younger series 

 of schists (the Vaikrita systemf) . Haydenf states that the granite-gneiss 

 is intrusive in Cambrian and Permian strata, and that certain schists 

 assigned to the Vaikrita system are altered Cambrian slates and quartzites. 

 In the Peninsula region of India gneisses have been distinguished as older 

 and younger, but without sufficient basis in observed relations, according 

 to Oldham. No distinctly sedimentary pre-Cambrian rocks are known 

 there. 



Thus we are not as yet able definitely to distinguish metamorphic 

 Proterozoic rocks in south China or India in such a way as to draw a 

 parallel with the Wu-t'ai schists. 



* Explorations des Gttes de Combustibles de 1'Indo-Chine, Annales des Mines, 8 ser., Mm. 2, p. 205. 

 fGriesbach: Geology of the Central Himalayas, India Geological Survey Memoirs, xxm, p. 40. 

 t Geology of Spiti, India Geological Survey Memoirs, xxxvi, pt. i, p. 8. 

 Manual of Geology of India, page 23. 



