CLIMATE AND PHYSICAL CONDITIONS OF KEEWATIN 5 



periods; though the rocks are of course far more altered by meta- 

 morphism. 



The Keewatin of the states near Lake Superior is described as 

 consisting almost entirely of eruptives such as have been referred 

 to above, though bands of iron range rocks occur with them in 

 Minnesota. President Van Hise and others therefore look on the 

 Keewatin as essentially eruptive with the exception of the oldest 

 iron ranges. 



It will be shown in succeeding pages that this is by no means 

 true of the Keewatin of Ontario. 



KEEWATIN SEDIMENTS 



When Lawson began his study of the Lake-of-the- Woods region 

 he was specially impressed, with the wide-spread eruptives and ash 

 rocks, though he found associated with them subordinate amounts 

 of sediments such as carbonaceous slates and quartzites; and he 

 defined the Keewatin as essentially an eruptive series. As his 

 work extended eastward, however, he made the acquaintance on 

 Rainy Lake of a great series of sedimentary rocks, to which he gave 

 the name of Couchiching. 



The correlation committee which adjusted the terminology of 

 the western Great Lakes region chose the name Keewatin instead 

 of Couchiching for the whole series; so that the Keewatin as now 

 defined includes both eruptives and sediments older than the 

 Laurentian. 



By Lawson and later workers in northern Ontario it has been 

 shown that every type of water-formed sedimentary rock is rep- 

 resented in the Keewatin: limestones and dolomites, carbonaceous 

 and ordinary slates, mica schist and gneisses representing more 

 altered muddy sediments, quartzites, arkoses, and graywackes, and 

 even conglomerates and breccias, though the last-mentioned 

 rocks are not always easily separated from agglomerates, etc., of 

 volcanic origin. 



With the exception of the Couchiching, most of these sedi- 

 mentary rocks are not extensively developed in the region studied 

 by Lawson; iron formation occurs only in small outcrops and 

 remained unobserved in the hasty field work of early days. 



