GEOLOGICAL AND NATURAL HISTORY SURVEYS. 169 



boundnry between them "is nearly defined by the course of the St. 

 Mary River." 



Speakin<>: of the primary rocks he says they commence at the con- 

 traction of the Montreal Channel of St. Mary River, across the 

 northern part of St. Joseph Island, the southeasterly end of Sugar 

 Fsland, skirt the easterly side of Great Lake George, forming a 

 range of hills, Avhich, from the head of the lake, passes to Gros Cap 

 of Lake Sui)erior. The primary region thus bounded stretches 

 nortlnve^terl}? "many himdred miles, skirting a portion of the shores 

 of Lake Superior, and, in conjunction v^ith the trap rocks, consti- 

 tuting t}ie hJghlands between th.at lake and Lake of the Woods. 

 From these highlands it stretches a little east of Lake Winnipeg, far 

 io the nortlnvest, finally constituting the immense ' barren grounds ' 

 of tlie British possessions. It is also well knoAvn that this range of 

 primary- rocks stretches in an easterly direction, through the interior 

 of the upper province of Canada.-' 



After devoting a couple of pages to the surface characters of the 

 primary rocks within the limits of Michigan, he proceeds to the 

 "sedimentary rocks." 



The "Lake Superior Sandstone" extends along the south shore 

 of the lake with continuity unbroken, except " by the occurrence of 

 a, comparatively limited range of primary and trap rocks." In its 

 easterly prolongation it rests against and upon the primary range 

 of St. Mary River, while on the south it is seen to pass beneath 

 th.e limestone. He pronounces the sandrock unfit for use in the 

 construction of the St. Mary Canal. This formation, thin on the 

 east, increases westerly to a thickness of several hundred feet. He 

 reports it entirely destitute of fossils. 



The formations overlying the sandstone have a slight dip in a 

 direction east of south. Thus, while these rocks dip in such a man- 

 ner as to form the basins of Lakes Huron and Michigan, their up- 

 raised edges form, as it were, the barrier that sustains the waters 

 of Lake Superior at their present level (p. 16). These forma- 

 tions are divided into two groups distinguished by their fossil re- 

 mains and chemical character, though the line of junction is not 

 readily traced. " The lower limerock and shales " are first con- 

 sidered. These are admirably exposed on the southerly shore of 

 Little Bay du Noquet and pass inland and as far eastward as Drum- 

 mond Island, thinning in their progress and losing their shale*;. The 

 upper limerocks overlie Drummond Island and line the lake shore 

 westward to the southerly cape of Green Bay. He thinks they rep- 

 resent three divisions: "The lower or Pentamcrus portion; the mid- 

 dle or polypiferous portion, and the upper or Mackinac and Mani- 

 toulin portion." These three divisions are well discriminated at 



