206 THE CANADIAN NATURALIST. [Vol. viii. 



lake, or about 23 feet above Lake Erie. Evidently, therefore, 

 a very slight rise in the bed of Niagara river would raise the 

 level of the three lakes and cause their waters to flow south- 

 into the Mississippi rather than north-east into the Atlantic. 



But great as these changes in the physical geography of the 

 country appear, they are geologically trifling. The general 

 surface was then as it is now. No new mountains have risen, and 

 little progress has been made in the destruction of old ones. 

 The great midland valley extended from the Alleghany Moun- 

 tains westward, and was drained by the Mississippi, the Father 

 of Waters in age not less than size. The Adirondacks, the 

 Laurentides, the Green and White Mountains, the Catskills, and 

 the Helderberg range then stood as now, while along the eastern 

 border of the Continent the Alleghanies and the Blue Ridge 

 formed its Atlantic frontier, their western slopes being drained 

 by the Ohio and its tributaries, flowing at least a hundred feet 

 below their present level.* 



* The substance of this paper was delivered before the Cincinnati 

 Natural History Society in January, 1875, and illustrated by a map 

 which is not reproduced here. The argument however appears in- 

 telligible without its aid. 



