CHAPTER II. PROTEROZOIC. 



PROTEROZOIC STRATA. 



We recognize two principal systems of stratified rocks of the Protero- 

 zoic era in northern China, the Wu-t'ai and the Hu-t'o or Nan-k'ou systems. 

 The Wu-t'ai was observed and named by von Richthofen ; the other he did 

 not distinguish from the Sinian, of which he thought it a conformable part, 

 and he described it as "Untersinisch." In certain sections and probably 

 generally, there is an unconformity between the "Untersinisch" and the 

 "Obersinisch," and it seems desirable to separate them by restricting the 

 term Sinian to upper or Obersinisch and giving a new name to the lower 

 or Untersinisch.* Nan-k'ou is an appropriate name, which may be applied 

 if we correctly understand von Rich thof en's section at the celebrated pass 

 northwest of Peking. Hu-t'o is a name we gave to a series which is 

 probably the equivalent of the Nan-k'ou, though it differs somewhat in 

 the character of the strata. The matter is discussed in a later paragraph. 



Proterozoic rocks are best exposed in China, so far as yet known, in a 

 mountain range in northern Shan-si, called the Wu-t'ai-shan. This name, 

 which means Five Platform Mountains, is derived from the five highest 

 summits in the region, Pei'-t'ai or North Table having an altitude of 10,045 

 feet. The range is deeply incised, and the canyons expose remarkably 

 distinct sections of ancient metamorphic rocks, comprising the basal or 

 T'ai-shan complex (Archean) and the Wu-t'ai system, eo-Proterozoic. 

 The latter is thought to be roughly correlative in age and duration and 

 complexity with the Huronian of Canada. 



On the southeastern flank of the Wu-t'ai-shan is a wide area of hills 

 and valleys, which we have called the Northern Loess Basins. The general 

 altitude is 3,500 to 5,000 feet above sea. Rocks of the early Proterozoic, 

 Wu-t'ai, system constitute part of the surface, but a younger pre-Cambrian 

 system of but slightly altered quartzites, slates, and siliceous limestones 

 covers a larger area. This neo-Proterozoic system we have called the 

 Hu-t'o, a local name, which may ultimately be replaced by the term Nan- 

 k'ou of von Richthofen or that of Nan-shan of Loczy. 



In view of the better, though still incomplete, knowledge which we 

 have of the Proterozoic in the Wu-t'ai as compared with notes of occur- 

 rence of similar rocks elsewhere, we may take the Wu-t'ai sections as types. 



*In a personal conference in Berlin, March, 1905, von Richthofen agreed orally to the desirability of 

 making this distinction, but his views were not put in writing, so far as I am aware. 



