MIDDLE PALEOZOIC, CENTRAL CHINA. 55 



Black chert, "lydite"; a characteristic stratum which does not, however, always 



occur in its place; checks on weathering into small angular fragments; thickness 



5 feet, 1.5 meters. 

 Green shale with numerous nodules of gray to brown ferruginous limestone: 100 feet, 



30 meters; highly fossiliferous, middle Ordovician (Trenton) fauna. 

 I/ight-gray to bluish limestone, in layers 2 to 6 inches thick, containing Orthoceras and 



coiled gastropods, lower Ordovician ; upper part of the Sinian (Ki-sin-ling) limestone. 



The characteristic green shales of the middle Paleozoic occur in typical 

 development on the Yang-tzi-kiang, in longitude 110 45' E., at the village 

 of Sin-t'an, and the name is conveniently used to designate the sequence of 

 strata between the Ki-sin-ling (Sinian) limestone below and the Wu-shan 

 (Carboniferous) above. Transition beds 200 feet, 60 meters, thick connect 

 the Ki-sin-ling and Sin-t'an and are characterized by upper Ordovician 

 fossils. The top of the Sin-t'an is marked by a distinct but conformable 

 contact of shale with the overlying massive Wu-shan limestone. 



From the limits stated it will be seen that the Sin-t'an formation rep- 

 resents all of Silurian (Gothlandian) , Devonian, and lower Carboniferous 

 time. Including the upper Ordovician transition beds, it is but 2,000 feet, 

 600 meters, thick, and as a whole is a rather monotonous clayey, sandy 

 deposit, modified by more or less calcareous, ferruginous, or bituminous 

 admixture. We were not able to detect any evidence of unconformity at 

 the base or top of the formation, nor within it. We regard it as a unit in 

 a complete sequence of strata; but it was evident that sedimentation was 

 meager during most of the periods represented. While it is possible that 

 the deposit accumulated chiefly during some particular epoch, we have no 

 clue to that one. 



The fauna found in the limestone nodules in green shale, and in light- 

 gray limestone near by is described by Weller in volume ill of this series. 

 It affords a sound basis for correlation with the Trenton limestone of the 

 United States and the Vaginoceras limestone of the Baltic, the relations 

 being closer with the latter. The horizon falls in the middle Ordovician. 



Although we repeatedly crossed the strata equivalent to this fossilifer- 

 ous bed, both north and south of Sii-kia-pa, none of the party observed 

 the fossils at any other locality. We may have overlooked them, especially 

 in running the swift current of the Ta-ning-ho and -Yang-tzi-kiang in boats, 

 but it is probable that the fossiliferous calcareous-, nodules in the green 

 shale are of occasional, not general, occurrence. Where they do occur the 

 fossils are conspicuous. 



In general the Sin-t'an formation is apparently unfossiliferous. Its 

 bituminous phases have much the character of the middle Devonian shales 

 of the eastern United States, and where green and sandy it suggests the 

 Chemung. 



