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actual diminished elevation of the land itself. In other words, the land 

 has been subsequently subjected to an upheaving force, which at last 

 has elevated the whole far above the influence of the sea. 



"Whether the upheaving of the land was general at this era, through- 

 out the continent, or was mainly operative in the region of the lates, 

 probably cannot be satisfactorily determined. It may be competent, 

 however, to suppose that these apparent " lake ridges" were the boun- 

 daries of the ancient sea, formed during intervals of rest in the upward 

 tendency of the land. The comparatively quiet state of the elements, 

 and the greater length of time for which the waters covered the extent 

 described, will satisfactorily account for the unifonnity of surface which 

 characterizes the country bordering on the present lakes, and those vast 

 plains of the west, which were subjected to the same influencing cir- 

 cumstances. 



There are, however, some reasons for concluding that a part, at least, 

 of this area, was occupied by fresh water, and to this supposition we shall 

 advert hereafter. 



There also exist strong reasons for supposing that the relative levels 

 of the land did not everywhere remain the same, or that disproportion- 

 ate elevations took place. Thus, appearances warrant the suppostion 

 that at several points baniers existed to that free communication which 

 I have assumed, of the water of this inland sea with the Atlantic. If 

 'we suppose the great Appalachian range of mountains, at any of the 

 points where it meets the St. Lawrence, to have once fonned a barrier 

 to that river, a communication through from the ocean in that direc- 

 tion, would have been cut off". The "Up Lifts," at Little Falls, 

 "which rise 14'7 feet higher than Lake Erie, and the " Highlands" of 

 the Hudson might also have interposed barriers to an outlet across the 

 State of New York. A single communication only would then exist 

 with the ocean, viz : through the valley of the Mississippi. That the 

 lakes once discharged their waters in this direction, such additional evi- 

 •dence is furnished by the appearance of the countr}-, that in this 

 our argument but serves to add confirmation to the general opin- 

 ion. 



There is further reason to suppose that a barrier has existed across 

 the Strait of Mackinac, cutting off" Lake Michigan, and perhaps Lake 

 Superior, from the lower lakes. Now, if we supposed that the erection 



