CHAPTER II. 

 TOPOGRAPHY OF THE BASIN OF LAKE AGASSIZ. 



The area that was covered by Lake Agassiz occupies the geographic 

 center of the North Americau contiueut. Its extent is approximately from 

 45° 30' to 55° of north hititude, and from 92° 30', on the international 

 boundary, to 106°, on the Saskatchewan River, of west longitude. 



If we consider the contour of the entire continent, it is seen to include 

 on the east and west two mountainous regions and between them a compai'- 

 atively flat expanse, at the middle of which Lake Agassiz lay. The eastern 

 mountainous tract stretches from Labrador southwestward to Alabama, 

 culminating in the Laurentide highlands north of the River St. Lawrence, 

 the White Mountains and the Adirondacks, the Green Mountains and the 

 Catskills, and the parallel Appalachian ranges farther southwest. The 

 si;mmits of this mountain belt vary in elevation from a half mile to one 

 mile and slightly more above the sea-level. On the west, a longer and 

 wider region of mountains, including generally three L>r four lofty parallel 

 ranges, extends from the northern and southern coasts of Alaska south- 

 easterh' and southerly tlnough the Canadian Northwest Territory, British 

 Columbia, the western thnd of the United States, Mexico-, and Central 

 America, to the Isthmus of Panama ; and beyond this it continues south in 

 the great Andes range along the entire western coast of South America to 

 Cai)e Horn. In the United States this Corddleran mountain belt includes 

 the Rocky Mountains and the Sierra Nevada and Coast ranges, and its 

 highest summits are nearly 3 miles above the sea,. 



Lake Agassiz, situated on the central expanse between these moun- 

 tainous regions, was a fifth of a mile above the present sea-level. WTiere 

 the slow northward ascent from the Gulf of Mexico ceases at a distance of 

 1,100 miles from the Gulf and an elevation of about 1,100 feet, and is 

 succeeded farther north Ijy a descending slope toward Hudson Bay, the 



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