368 PALEOZOIC ROCKS OF THE HUDSON BAY REGION 



described above indicates the age of the Severn Eiver limestone as about 

 that of the Cataract formation of Ontario, which probably corresponds in 

 age to the early Brassfield or Sexton Creek time. The relations of the 

 province in which the Severn Eiver limestone was deposited to the other 

 North American marine provinces of this time, as conceived by the 

 writers, is shown on the paleogeographic map, figure 2. 



Ehwan River limestone. — The Ekwan Eiver limestone doubtless corre- 

 sponds in age to the lower or middle part, or to both the lower and middle 

 parts, of the Lockport, or Louisville, limestone of the Mississippi Valley 

 and New York State, but it belongs to a different province of deposition, 

 in which the fauna was so different as to make direct correlation with any 

 horizon of the Lockport unusually difficult. It appears to be younger 

 than the Clinton of New York, and to be equivalent in time to the lower 

 or middle Lockport limestone of the Niagaran series, as the succeeding 

 Silurian rocks in the Hudson Bay region are thought to represent late 

 Lockport time. 



Attawapiskat coral reef. — The Attawapiskat coral reef is thought to 

 correspond, in part at least, with the reef rock referred to by William 

 Logan,^^ and more recently described by Williams^^ as the Eramosa beds, 

 which occurs in the upper part of the "Lockport member of the Niagara" 

 in southern Ontario. 



While the Ekwan Eiver limestone and the Attawapiskat coral reef are 

 thought to correspond in time to some part of the Niagaran epoch, the 

 conspicuous feature of the Niagaran rocks in the Hudson Bay region is 

 the great difference in the character of their faunas compared with that 

 of the Niagaran in the Mississippi Valley and New York. Very few of 

 the typical Niagaran species of the latter areas are present in the Niag- 

 aran rocks of the Hudson Bay region. Not a single species of Niagaran 

 brachiopods is common to the Hudson Bay region and the Iowa and Illi- 

 nois region of the Mississippi Valley, and no species of Echinodermata, 

 MoUusca, or Arthropoda found in one of these areas has been definitely 

 identified in the other. A few of the Silurian corals that have an almost 

 world-wide distribution appear in both regions, but many of the coral 

 species present in the northern area do not appear in the southern. 



The Niagaran fauna of Illinois and Iowa resembles that of the Niag- 

 aran of New York so much more closely than either one of these resem- 

 bles the Niagaran of the Hudson Bay region that it seems much more 

 probable that the Niagaran fauna of Illinois and Iowa came from the 



^8 William Logan : Geol. Surrej- of Canada. Report of progress to 1863, p. 337. 

 18 M. Y. Williams : An Eurypterid horizon in the Niagara formation of Ontario. Geol, 

 Survey of Canada, Mus. Bull. no. 20, Geological series no. 29, 1915. 



