170 Professor H. D. Rogers, on the Geology and [Feb. 8, 



lakes only expansions of the Upper St. Lawrence, their southern 

 watershed then taking its true half-way position below the G ulf of 

 St. Lawrence and the Gulf of Mexico. The basin of the five lakes 

 is a wide level plateau falling eastward, by successive stages, from a 

 level at the surface of Lake Superior of 628 feet, to one of 232 feet 

 at the surface of Lake Ontario. Its confining watersheds are only 

 the eastern extensions of the great central swell of the Continent, 

 forking where it approaches Lake Superior ; one branch ranging 

 northward, the other southward, of this long and narrow basin. 



3. The Hudson Bay Basin.— This almost rivals in size that of 

 the Mississippi. It is separated from that of the St. Lawrence by a 

 low, crescent-shaped, curving watershed, beginning in the highlands 

 of Labrador and the Watchish Mountains, and extending westward 

 in the Missabay Heights. To the south-west and west its boundary 

 is the vaguely-traced limit of the western plateau, prolonged north- 

 north-west from the Missouri towards Lake Athabaska. This great 

 basin is a region of innumerable tortuous streams and inosculating 

 lakes and swamps, converging their drainage into Hudson Bay. In 

 the northern half of the continent, the larger rivers which enter 

 Hudson Bay, as the Great Saskatchawan, descend from the base of 

 the Rocky Mountains, across the low watershed which forms the 

 western rim of this basin ; thus linking it hydrographically with 

 the high western plateau, and establishing, in a wider sense, one 

 great hydrographic basin from the Watchish to the Rocky Moun- 

 tains, north of the east and west swell of the continent. The general 

 elevation of the extensive rim of the Hudson Bay Basin is scarcely 

 anywhere higher than 1600 feet above the sea ; the average level of 

 the whole girdle probably not exceeding 1000 feet. It is a cold, 

 inhospitable, and snowy district, its rocks deeply overlaid with sterile 

 drift, and its surface extensively covered with a network of waters 

 and wet swamps. 



B. The Appalachian Mountain Zone. 



This Atlantic mountain range embraces the whole belt of moun- 

 tain ridges extending from the Gulf of St. Lawrence at Gaspe, to 

 Georgia and Northern Alabama. It consists of two divisions— a 

 north-eastern, ranging from Gaspe to the valley of the Hudson ; 

 and a south-western, thence to the interior of Alabama : the total 

 length of the chain is about 1500 miles, while its breadth varies 

 from 150 to 200 miles. In the chief divisions of its length it is a 

 wide complex belt of many parallel ridges, whose crests nowhere 

 ascend much beyond 4000 feet above the sea ; the base of the chain, 

 where highest, being about 1800 feet above the sea level. From 

 Alabama to the Hudson, the Appalachian chain is the watershed 

 between the Atlantic rivers and those of the Ohio and Lake 

 Ontario ; and from the Hudson to the Gulf of St. Lawrence it 

 separates the drainage of those flowing to the Atlantic from the 

 shorttt* streams entering the St. Lawrence. The Hudson valley 



