342 PALEOZOIC ROCKS OF THE HUDSON BAY EEGIOX 



Thickness 

 in feet 

 of northern Michigan, and the upper part of the Silu- 

 rian rocks west of Lake Winnipeg; with the Cataract 

 formation of Ontario, and the Sexton Creek and Brass- 

 field limestones of the Mississippi Valley 75 



Port Nelson limestone 



Correlated with the basal part of the Stonewall limestone 

 of western Manitoba, especially the lower part of the 

 Silurian exposed in the vicinity of Grand Rapids of 

 Saskatchewan River ; with the upper part of the May- 

 ville limestone of Wisconsin, and with the lower part 

 of the Silurian limestone in Alaska, Utah, and western 



North America About 35 



Ordovician system 



Cincinnatian series 



Shammattawa limestone 



Correlated with the Upper Ordovician (Stony Mountain) 

 limestone in the vicinity of Lake Winnipeg ; the Fish 

 Haven dolomite of Utah; the Bighorn dolomite of 

 Wyoming, and the upper and middle parts of the Fre- 

 mont limestone of Colorado. Equivalent in time to 

 some part of the Richmond and Maquoketa of the Ohio 



and Mississippi valleys 75 to 80 



Mohawkiau series 



Nelson River limestone 



Correlated with the lower Ordovician rocks of the Lake 

 Timiskaming region ; the Winnipeg limestone in the 

 vicinity of Lake Winnipeg. About equivalent in time 

 to the Galena limestone of the upper Mississippi Valley 

 and the Trenton limestone of New York and eastern 

 Canada About 70 



• Ordoviciax Eocks IX THE HuDsox Bay Eegiox 



LOCATION 



The main body of Ordovician strata in the Hudson Bay region occurs 

 in the northern part of the sedimentary area where they outcrop in a 

 broad, roughly crescentic belt that is bounded on the west by pre-Cam- 

 brian crystallines and on the east by the Silurian strata which lap on 

 them or in places transgress them in a westward direction. 



EARLIER STUDIES 



Ordovician rocks on the Xelson and Churchill rivers were briefly de- 

 scribed bv Bell- in 18 79. On the basis of the very few fossils collected 



- Robert Bell : Report on explorations on the Churchill and Nelson rivers and around 

 God's and Island lakes. Geol. Survey of Canada, Summary Kept., 1878-1879, pp. 1-72C. 



