CLOSE OF THE PROTEROZOIC. 29 



Late Proterozoic strata are not known in Shan-tung, which seems 

 to have formed an eastern shore of the strait in which the Nan-k'ou lime- 

 stone was deposited. Nor have they been noted elsewhere in Asia outside 

 of Tibet, unless some of the rocks of western Yiin-nan, which Loczy assigned 

 to the Nan-shan terrane, prove to be of that age. 



In their typical occurrence in northern Shan-si, Hu-t'o strata are dis- 

 cordantly overlain by the earliest Sinian (Cambrian) sediments. The older 

 rocks were evidently folded and eroded to a peneplain, over which the 

 Sinian sea transgressed. Where we observed the Sinian in relation to the 

 Nan-k'ou limestone (at Nan-t'ang-mei', Chi-li) an unconformity is indicated 

 by a basal conglomerate of chert.* A discordance of dip was not observed, 

 but probably exists; yet the strata may be parallel. There are no other 

 observations which enable us to determine the area affected by the post- 

 Nan-k'ou pre-Sinian disturbance. The effects may be looked for through- 

 out that littoral zone in which the type locality lies and which probably 

 extends along the Kuen-lung system. The movement did not compare in 

 intensity with that which closed the Wu-t'ai period; and even though it 

 should ultimately be found to have affected an extensive belt, we can not 

 assign to the epoch of deformation and consequent erosion a duration at 

 all equivalent to that of mid-Proterozoic diastrophism. Nevertheless, 

 it appears to mark a break in continental history equivalent to that at the 

 base of the Cambrian in North America, and consequently to be properly 

 regarded as the last episode of the pre-Cambrian, immediately antedating 

 the Sinian transgression and the advent of that Lower Cambrian fauna 

 which is abundantly preserved in the Sinian deposits. The limitation of 

 the term Sinian to a Cambro-Ordovician system is discussed in the next 

 chapter. 



Our present knowledge of pre-Cambrian diastrophism in eastern Asia 

 may be summed up as follows : During very early times movements which 

 are expressed in schistosity and metamorphism of the most ancient rocks 

 occurred in a deep-seated zone. The superficial effects of the compressive 

 movements are lost; that is, the fractured and simply folded rocks of that 

 early time were eroded and the schists were exposed. The wide-spread 

 occurrence of the Archean schists shows that epeirogenic movements were 

 general. Of localized erogenic phenomena we have no direct evidence, 

 yet we can not doubt that they also developed in a commensurate scale. 

 The axial trends of Archean rocks are north-northeast (the Baikal direc- 

 tion) and west-northwest (the Saian bearing). These meet south of the 

 amphitheater of Irkutsk, and further south are connected by the trends 

 which correspond with the Altai ranges of northern Mongolia. 



* Vol. I of this report, p. 131. 



