Vol. I. C. C. Yu — Ordovician Cephalopoda of Central China (ii) 21 



Silurian 



Hiatus and disconformity 



Ordovician 



Brachiopod shale 



Hiatus and disconformity 



Trinucleus shale 



Chasmops beds, dark shales with graptolites and numerous concretionary 

 limestone masses and beds of impure limestone containing Chasmops 

 sp., Echinosphieriies aurantinum Gyjlenh. 



Orthoceras limestone 



(d) Upper gray or Chiron limestone 

 (c) Upper red limestone 

 (b) Lower gray or Asaphus limestone 

 Hiatus and disconformity .... J 



)- Upper Llandeilan 



Lower Didymograptus shale \ ^ a • • 



•^ " -^ Y Lower Arenigian 



Planilimbata limestone 



(a) Lower red or Limbata limestone ^ 



Y 



Hiatus'} j 



Cambrian 



Formerly the name of "Orthoceras limestone" was applied to a Umestone 

 series included within the graptolite-bearing shales of the Ordovician and 

 since the Lower Didymograptus shale (Phyllograptus shale) is early Arenig, the 

 Orthoceras limestone was also referred to the Arenig. Since there is a hiatus exist- 

 ing between the Lower gray or Asaphus limestone and the Lower red or Limbata lime- 

 stone, the latter is now united (when the Lower Didymograptus shales are absent) with 

 the Planilimbata limestone, the combined series being called "Megalaspis limestone". 

 The name "Orthoceras limestone" is now restricted to the 3 limestones overlying the 

 hiatus, namely the Lower gray limestone, the Upper red Umestone and the Upper gray 

 limestone, and these represent the later Llandeilan or late Middle Ordovician age. From 

 the "List of the Fossil Faunas of Sweden" we find that the species Vaginoceras (End.) 

 wahlenhergi Foord, Vaginoceras [End.) vaginatum Schloth, and some other forms were 

 actually found in the Lower gray Orthoceratite Limestone,' in other words they occur 

 in the same horizon as in China. Foord's statement, of course is not correct. 



I. G. Lindstrom: List of the Fossil Faunas of Sweden, I., pp. 9-10. 



