200 THE CANADIAN NATURALIST. [Vol. viii. 



Lake Superior is of comparatively recent date. Not only do the 

 descriptions of this tract by Messrs. Foster and Whitney confirm 

 this inference, but examinations of the district since made by 

 Mr. Wadsworth of the Michigan Geological Survey, almost 

 directly demonstrate the former outlet of Lake Superior to have 

 been through the White Fish valley." " It appears that the 

 outlet of Lake Superior was through little Bay de Noc up to the 

 close of the Tertiary age." Of course we are as yet unable to 

 give the depth of this channel, but considering the change of 

 elevation it is not improbable that we have here the pre-glacial 

 outlet from the valley, and that Lake Superior then existed as a 

 vast, open, almost level plain, through which flowed a river to 

 the southward. We incline however to think that instead of 

 leading into the valley of Lake Michigan, as Mr. Winchell sup- 

 poses, this river flowed more to the south-westward, through 

 Lake Winnebago and Lake Horicon by the valley of Rock River, 

 and met the Mississippi near where Rock Island now lies. In 

 confirmation of this view we cite the following : 



" The State of Wisconsin is traversed by a remarkable valley. 

 Commencing north of Lake Michigan, near Lake Superior, this 

 depression runs south west, and contains in its northern part the 

 waters of Green Bay, and in its southern portion those of Rock 

 River. It pursues an almost straight course for 400 miles and 

 terminates on the Mississippi, where Rock River flows into it. 

 From the northwest the country descends by a gentle slope into 

 the valley, but from the south-west it breaks down suddenly and 

 often by a perpendicular precipice. A rocky ridge, the Upper 

 Silurian escarpment spoken of above, or rather an elevated region 

 of Silurian rock, some 300 feet in height, separates this valley 

 from Lake Michigan." E. Andrews, M.D., in Am. Journal of 

 Science and Arts for September, 1£69.* 



The condition of the Michigan valley during the same era 

 was similar to that of the valley of Lake Superior. In the geo- 

 logy of Ohio (Vol. 2, p. 13), we read : " An excavated trough 

 runs northward " (southward) " from Lake Michigan to the 

 north line of Iroquois county, Illinois, thence south-west through 



* We may mention here that Mr. Gr. M. Dawson in his recent 

 report on the geology of part of the region near the 49th parallel, 

 states his belief that in pre-glacial times Lake Winnipeg also had a 

 southern outlet. 



