ORDOVICIAN 343 



by Bellj Whiteaves referred these rocks to the Trenton limestone and 

 considered them the equivalents of the Galena limestone of Wisconsin 

 and Illinois. The Ordovician limestones outcropping on Churchill River 

 overlie a massive, dark gray quartzite which outcrops at the mouth of 

 this river and which Bell compared with the gold-bearing lower Cambrian 

 quartzites of Nova Scotia, while along the Nelson River these limestones 

 rest on Avhat are thought to be pre-Cambrian crystallines. 



The geology of the Nelson and Churchill rivers has been more recently 

 treated by Mclnness/ who summarized the results of Bell's work and 

 discussed additional data gathered by himself. His studies of the sedi- 

 mentary rocks were meager, and little new of importance was added. 



In the report of the Hudson Bay exploring expedition of 1912 by J. B. 

 Tyrrell,* the Ordovician rocks on the Shammattawa, a branch of Hayes 

 River, were described and a list of fossils identified by Parks was given, 

 on the evidence of which the rocks were considered about the age of the 

 top of the Trenton of eastern Canada. 



The presence of Ordovician rocks much farther south was shown by 

 Whiteaves from a study of fossils collected by Wilson^ on the Drowning 

 and Little Current rivers, two tributaries of the Kenogami, a branch of 

 the Albany River west of James Bay. 



From fossils collected near the head of Frobisher Bay, Schuchert^ has 

 demonstrated the presence of corresponding Ordovician strata as far north 

 as Baffin Land. 



PRESENT STUDIES 



The present studies of the Ordovician rocks in the Hudson Bay region 

 were confined to outcrops along Nelson and Shammattawa rivers and a 

 few of their tributaries. 



Outcrops of Ordovician limestone and dolomite occur at intervals in 

 the banks of Nelson River for a distance of about 22 miles. The oldest 

 strata are exposed farthest west — about 95 miles above the mouth of the 

 river and only a short distance east of an outcrop of crystalline rock — 

 but the contact of the limestone with the crystallines was not seen at this 

 place. These limestones include strata corresponding in age to the latter 

 part of the Mohawkian epoch, about the time of the Galena dolomite, and 



^ William Mclnness : The basins of Nelson and Churchill rivers. Canada Dept. of 

 Mines. Mem. no. 30, 1913, pp. 1-142. 



* J. B. Tyrrell : Hudson Bay exploring expedition. 22d Kept. Ontario Bureau of Mines, 

 1913, pp. 188-239. 



s W. .T. Wilson: Geological reconnaissance of a portion of Algoma and Thunder Kr, 

 districts, Ontario. Canada Geol. Survey, 1909. pp. 49 and ff. 



6 Charles Schuchert : Proc. U. S. Nat. Mus., vol. xxii. 1909. pp. 143-177. 



