

TYPE SECTION OP SINIAN. 37 



applied in Europe and America. It is, moreover, possible that the formation in China, in 

 which strata containing the primordial fauna have indeed a definite but somewhat subor- 

 dinate position, reaches much further down and therefore comprises a much longer period, 

 while it also probably extends without noticeable interruption up into the lower Silurian. 



SINIAN IN CHINA. 



When asked to suggest a district in which the Sinian might be studied 

 in typical character, von Richthofen referred us to I/iau-tung and Shan- 

 tung, the northeastern provinces of China. The conditions immediately 

 preceding war rendered surveying in L,iau-tung difficult at the time of our 

 expedition, and Shan-tung became the scene of our detailed studies. 



The Ch'ang-hia and Sin-t'ai districts which were selected for detailed 

 topographic and geologic surveys are represented in plates xin and xiv, 

 volume i, and the local variations of strata are described by Blackwelder, 

 volume i, chapter n. The general sequence consists of three well-defined 

 divisions between two unconformities, as follows: 



Unconformity by erosion. 



Tsi-nan limestone (lower Ordovician). 



Kiu-lung group, interbedded limestone and shale (Upper and Middle Cambrian) . 



Man-t'o shales (Middle and late Lower Cambrian). 



Unconformity by dip. 



Pre-Cambrian rocks. 



Lower Sinian. In Shan-tung, Ljau-tung, and Shan-si, that is, through- 

 out northern China, the characteristic strata of the Lower Sinian are red 

 deposits, which we have called the Man-t'o formation. They are probably 

 equivalent to von Richthofen's Tung-won Schichten. In Central China, on 

 the Yang-tzi-kiang, we saw nothing corresponding to the Man-t'o formation, 

 the Sinian being composed of limestone, apparently to the very base. 



The typical red shale of the Man-t'o formation passes into red or 

 chocolate-brown shaly sandstone and is interbedded with thin but some- 

 times persistent layers of gray to cream-colored limestone. The thick- 

 ness varies from 350 to 550 feet, 105 to 165 meters. The basal layers 

 occasionally show local conglomerates, as at Nan-t'ang-mei', Shan-si, where 

 a body of chert conglomerate rests upon cherty Proterozoic limestone, 

 and south of Tung-yu, Shan-si, where the underlying slates of the Hu-t'o 

 system constitute pebbles in the Man-t'o next the contact. Usually, how- 

 ever, the material adjacent to the eroded surface of pre-Cambrian rocks is 

 highly oxidized residual soil or fine calcareous sediment, which is in either 

 case foreign to the underlying metamorphic rocks. 



The sandy red mud of the Man-t'o formation is an end-product of 

 mechanical and chemical rock decay. Only the most enduring minerals, 



