626 NORTH AMERICAN INDEX FOSSILS. 



Mayville limestone. 



Iron Ridge ore (''Clinton"). 



(Small hiatus and dis conformity.) 



SUBFORMATION. 



Upper Ordovicic — Maquoketa shales. 



In eastern Iowa, the Niagaran is represented by the Delaware 

 limestone, rich in typical Niagaran fossils, and the Gower limestone 

 which comprises two phases, the LeClair limestone phase, probably 

 a reef facies, and the Anamosa phase. 



In southern Ohio, the Niagaran has been subdivided as follows : 



Hillsboro sandstone. 

 Cedarville limestone. 

 Springfield limestone. 

 West Union limestone. 

 Osgood beds. 

 Dayton limestone. 

 Clinton limestone. 



In the southern states the Siluric formations have a somewhat 

 different organic facies. In Illinois and Missouri, the Girardeau 

 or Alexandrian formation of early Lower Siluric age, rests accord- 

 ing to T. E. Savage,^' upon the late Ordovicic (Orchard Creek), 

 there being nevertheless a small hiatus. It is succeeded discon- 

 formably by the Edgewood and this in turn with another discon- 

 formity, by the Clinton. The Alexandrian probably represents a 

 southern invasion. Typical northern Niagaran strata overlie the 

 Alexandrian. In western Tennessee, the Niagaran is subdivided as 

 follows : 



Brownsport (Foerste).^^ 



Beech River (Pate and Bassler).^^ 



Bob. 



Lobelville. 

 Dixon. 



" T. E. Savage, American Journal of Science, XXV., pp. 431-44 and later 

 communications (Pal. Soc. Am.). 



^^A. E. Foerste, Jour. GeoL, Vol. XL, pp. 554-715- 



^^ W. F. Pate and R. S. Bassler, Proc. U. S. Nat. Mns., Vol. XXXIV., pp. 407-32. 



