20 RESEARCH IN CHINA. 



the broad zone of granite near "Jam-pa-quan," they appear to be intruded 

 by granite dikes, and are folded in such a way as to constitute anticlines 

 between which less highly metamorphosed strata, assigned to the Paleo- 

 zoic, appear in synclines. 



From the observations of Obrutchov, Loczy, von Richthofen, and 

 ourselves, in four parallel sections across the central and western Ts'in-ling- 

 shan, it thus becomes apparent that the geologic structure involves several 

 complex factors. There are metamorphic rocks, some of which are probably 

 pre-Cambrian, and among them may be representatives of the basement 

 gneisses as well as of the Proterozoic metamorphosed series. There are 

 other metamorphic rocks of Paleozoic and probably also of early Mesozoic 

 age, which vary in degree of metamorphism according to the intensity of 

 action incident to local folding and intrusion. And there are areas of 

 Paleozoic strata which exhibit little or no effect of metamorphism. These 

 various masses are closely folded, overturned, and overthrust, producing 

 relations as complex as some of Alpine structure. 



We may conclude that the occurrence of pre-Sinian rocks in the western 

 Ts'in-ling-shan is highly probable. Where such rocks are known in the 

 central Ts'in-ling-shan, they are chloritic schists with thin beds of quartz- 

 ite and marble, very closely resembling the strata of the Si-t'ai group of 

 the typical Wu-t'ai district. 



ANCIENT METAMORPHIC ROCKS BEYOND CHINA. 



Under this heading I propose to consider the relations of certain rocks 

 which are variously classified as Archean, Wu-t'ai, Sinian, early Paleozoic, 

 and Silurian, by observers in Tibet, Indo-China, and India. 



In Tibet they constitute the unfossiliferous pre- Devonian series of the 

 great Nan-shan mountain system, and have been observed by L6czy in 

 his journey along the northern base of the Nan-shan range, from Lan- 

 chou-fu to Sti-chou and return ; and by Obrutchov in his far more extended 

 journeys across southern Mongolia and back and forth among the several 

 great ranges of the Nan-shan. 



Under the heading crystalline schists,* Loczy says: 



The Archean complex of gneisses, mica schists, and phyllites plays a subordinate 

 r61e in those parts of the middle Kuen-lung chain which we traversed. In none of the 

 mountains which we crossed was I able to distinguish a crystalline axis. 



He then discusses at some length various occurrences of crystalline 

 schists, having in mind chiefly their eccentric position in the individual 

 ranges in which they occur, but gives little information concerning their 



*Reise des Grafen Sz&henyi, vol. I, p. 642. 





