80 RESEARCH IN CHINA. 



which, after the manner of lime deposits, presumably hardened in course 

 of accumulating, may be supposed to have been swept clean in a shallow- 

 ing gulf or strait until the current was checked and the terrigenous sedi- 

 ments from nearby land were laid down. It is evident that the strata 

 in contact with the limestone may be nearly continuous with it or indefi- 

 nitely younger than it. 



On the other hand, apparently at the other extreme of unconformity, 

 we have strata extended across eroded folds, with marked discordance of 

 dip. In a case described by von Richthofen and Loczy near Kuan-yuan- 

 hien in northeastern Ssi'-ch'uan, erosion has laid bare Silurian strata on an 

 anticline including several thousand feet of Paleozoics, and the overlapping 

 formation is possibly Permian, more probably Triassic limestone. There is 

 no doubt of folding, which resulted in a more or less elevated range, accom- 

 panied by erosion which reduced that range to a peneplain. The obscure 

 feature is the answer to the question: how does the unconformity consist 

 with the fact that in nearly adjacent regions strata are concordant in dip, 

 from Carboniferous to Jurassic; such being the case on the middle Yang- 

 tzi, in eastern Ssi'-ch'uan, 200 miles, 320 kilometers, distant.* I take it that 

 the phenomena illustrate two things which are by no means peculiar to 

 Central China. The first is that effects of folding are localized in linear belts 

 and may be very decided in certain zones which lie adjacent to others that 

 do not share in the disturbance; which remain, for instance, the bottoms 

 of deep synclinoria. And the other is that the growth and wasting of an 

 elevation due to folding takes no longer than the transition period from 

 Paleozoic to Mesozoic. How long that was it is difficult to say, but in geo- 

 logic terms it included the latest Carboniferous, the Permian, and part of 

 Trias, in Asia; and probably exceeded Pliocene and Pleistocene time, 

 judging by the effects of mountain growth and planation. 



PERMO-TRIASSIC STRATA. 



Angara series. There are in Asia two series of continental deposits 

 which are approximately contemporaneous, but are geographically distinct. 

 They both include members which range in age from Permian to Lower 

 Jurassic, and thus cover the Paleozoic-Mesozoic transition period. The one 

 is the well-known Gondwana series of the Indian peninsula, the other the 

 Angara series of Siberia and the Altai region. f Representatives of the 

 Gondwana series have been identified in Indo-China and also in Australia. 

 These districts lie south of the great central mediterranean of Asia, to which 

 Suess has given the name of Tethys, whereas the occurrences of the Angara 



* Research in China, vol. i, chapter xui, pp. 285 et seq. 

 f La Face de la Terre, Suess, vol. HI, p. 37. 



