100 RESEARCH IN CHINA. 



The oldest, the Pei'-t'ai cycle, links the physiographic history with the 

 stratigraphic record. We have seen that in the sediments there is reason to 

 regard the Cretaceous as a time when Asia presented the aspect of an exten- 

 sive peneplain, over which the sea transgressed from the south. Sediments 

 of the Eocene and Oligocene epochs record the same conditions. We regard 

 the Pei'-t'ai as the equivalent surface, and the Pei'-t'ai cycle as covering late 

 Cretaceous and early Tertiary. It is the Asiatic representative of the 

 Schooley or Kittatinny peneplain of the eastern United States and of the 

 Cretaceous peneplain of central Europe. 



The remnant of a peneplain which we recognized in Pe'i-t'ai by its form 

 and by the residual soil peculiar to it, is of very small extent, and we may 

 well ask what other evidences remain to support the inferences of a once 

 general condition. Let us proceed northeastward from the Wu-t'ai-shan, 

 which is in northern Shan-si, and review some known features, bearing in 

 mind that the ancient surface is both warped and eroded; consequently 

 it may occur at any altitude and may be more or less dissected. Where 

 the Siberian railroad, after leaving the dislocated mountainous region of 

 Trans-Baikalia, traverses northeastern Mongolia to the Khingan range and 

 descends into the valleys of Manchuria, there is a plateau surface which 

 is a slightly warped plain of erosion, occasionally capped by lava flows. In 

 the Khingan range it is warped a few hundred feet higher and, extending 

 over the crest, is represented in the summits of the long spurs which consti- 

 tute the deeply canyoned eastern slope. In Manchuria it sinks beneath 

 the alluvium of the Sungari, as the tilted peneplain that forms the western 

 slope of the Sierra Nevada of California sinks beneath the alluvium of the 

 Sacramento. 



Suess refers to the eastern slope of the great Khingan range in its north- 

 ern extension as being analogous to a flexure, and gives the following account 

 of the great plain of the Amur :* 



The constitution of the plain which extends northward from the upper Amur is not 

 altogether simple. Even at the eastern base of the Khingan, beds of the Angara series 

 appear * * * and occupy all the west of the plain * * *. They are covered 

 by white sands and shales with lignite of Tertiary age, which occupy the eastern portion 

 of the plain as far as the Zeia river * * *. But this mantle of Tertiary has in general 

 only a slight thickness; beneath it appear, as upon the upper Tygda, the Archean rocks 

 which play scarcely any orographic role. * * *. In the occasional outcrops of the 

 Archean basement M. Ivanov recognized the general strike of north-northeast, but accord- 

 ing to this observer the Angara strata which form the western part of the plain are not 

 horizontal; on the contrary, along the Amur, in the strip between the great Khingan and 

 the first outcrops of the Archean basement, they appear folded with the same north-north- 

 east strike. The plain owes its origin to the degradation of these folds. 



*La Face de la Terre, vol. m, p. 155. 



