28 RESEARCH IN CHINA. 



Wu-t'ai schists. Von Richthofen enumerates them* and nothing has been 

 added to his account except Blackwelder's notes on the Ta-ku-shan quartz - 

 ites. The facts do not suffice to fix any dates other than that one which 

 preceded late Proterozoic. In the great lapse of earlier time there were in 

 North America, and probably also in Asia, several cycles of erosion, sedi- 

 mentation, and orogeny, and the correlation on lithologic likeness is incon- 

 clusive. We believe the Wu-t'ai terranes to be divided by an unconformity, 

 and similar divisions probably exist elsewhere. Hence we can not establish 

 equivalency of the epoch of folding in Shan-tung with that which was so 

 decided in the Wu-t'ai, but in view of the intensity of effects in both regions, 

 a rough correlation has a presumption in its favor. 



The orogenic activity, which affected the Wu-t'ai rocks before any 

 later beds known to us accumulated, divides the Proterozoic of China into 

 two major periods. The earlier, the Wu-t'ai, links itself to the much 

 older Archean; the later, the Hu-t'o or Nan-k'ou period, is like the early 

 Paleozoic in general character. Whatever elevations resulted during the 

 dividing epoch of orogenic activity, they did not survive to deliver sedi- 

 ments to the Nan-k'ou seas. Except that they may be represented by 

 rocks which are not yet separated from the late Proterozoic, we must sup- 

 pose that the mid-Proterozoics were deposited beyond the confines of the 

 continent or in the deep synclinoria which in pre-Tertiary time traversed it. 



Strata of the Hu-t'o system in the typical district succeed the Wu-t'ai 

 after an interval represented by the profound orogenic activity described 

 in the preceding paragraph. The sequence of sediments ranges from 

 elastics of rather fine grain to carbonates; quartzites interbedded with 

 greater thicknesses of slates pass by transition upward into cherty lime- 

 stones. The total thickness is very roughly guessed at 5,000 feet, 1,500 

 meters. The elastics are terrigenous deposits, probably of the littoral 

 zone. The equivalent marine formations are the lower limestones of the 

 Nan-k'ou formation, of which the upper part is probably identical with 

 the limestone of the Hu-t'o system. The unconformity and succeeding 

 strata mark a transgression upon a flat land, which was sufficiently warped 

 to deliver to the coastal waters the sands and clays of residual and alluvial 

 deposits. Off shore, at a distance of 50 miles, 80 kilometers, or less, lime- 

 stone formed from the very inception of the transgression, and extended 

 landward as the sea widened. Such is the record for North China. If we 

 rightly correlate the Nan-shan sandstone, or that part of it which carries 

 the "early Paleozoic" limestones of Loczy, with the Hu-t'o system, the 

 evidence of similar shore conditions may be traced westward across Tibet. 



* China, vol. 11, p. 707. 



