12 BULLETIN 16 4, UNITED STATES NATIONAL MUSEUM 



DESCRIPTION OF THE FORMATIONS 



ORDOVICIAN SYSTEM 



Thus far three formations containing Ordovician faunas, the 

 Ssuyen, the Wuting, and the Kangyao have been delimited in South 

 Manchuria. 



BOUNDARIES OF THE ORDOVICIAN 



The top of the Ordovician Ssuyen formation is everywhere ap- 

 parently conformably overlain by the variegated siliceous shales 

 of Inai's Wuhutsui formation, which is likely of Carboniferous age, 

 although some geologists insist that it may represent the Silurian, 

 a view not accepted by most of the Asiatic geologists. 



If the Wuhutsui is really Carboniferous, it overlaps apparently 

 conformably on the Ordovician Ssuyen formation without trace of 

 the Devonian and Silurian. So far as we now know, nowhere in 

 South Manchuria, North China, or North Korea is there any physical 

 evidence of the unconformity between the Wuhutsui formation and 

 the underlying Ordovician Ssuyen. In the Kuantung district, 

 the Ordovician Wuting formation rests apparently conformably 

 on the Ozarkian, and in the Pechili district, the Kangyao overlies 

 the Ozarkian, while in the Tai-tzu district, the Kangyao formation, 

 which is subjacent to the Wuting, appears to rest on the Canadian 

 Santao formation. As yet, however, the exact contact between the 

 Kangyao and Santao has not been located. 



SSUYEN FORMATION 



Type locality. — Near Ssu-yen-kou, just north of the Pen-hsi-hu 

 colliery. (Pis. 2, 3.) 



Character. — The upper division is composed of moderately thick- 

 bedded, gray to light gray limestone intersected by many calcite 

 veins. In this uj)per section there are several irregular edgewise 

 conglomerates and thin dolomitic limestone beds. The lower por- 

 tion consists of moderately thick-bedded, light gray arenaceous, dolo- 

 mitic limestone. Two fossil-bearing horizons occur in the Ssuyen, one 

 in the uppermost part and the other near the base of the formation. 



Thickness. — As follows : 



Aigawa subdistrict 280 m (918.4 feet). 



Liaoyang-Yentai subdistrict, estimated about 200 m (656 feet). 



Pen-hsi-hu section 160 m (524.8 feet). 



Near Ilui-shan, 4 miles northeast of the Pen-h.si-hu col- 

 liery 160 m (524.8 feet). 



Niu-hsin-tai section, estimated about 200 m ((>56 feet). 



Hsiao-shih subdistrict, about 280 m (918.4 feet). 



