

NORTH AMERICA. 



about 32,000 square miles ; its surface is 600 feet 

 above that of the ocean, its mean depth upwards 

 of loco feet. It has, like all the others, no tidal 

 ebb or flow, is studded by few islands, and, from 

 the unsheltered nature of its shores, affords no 

 great facility for shipping. It discharges its sur- 

 plus waters by the river St Mary, which, after a 

 course of 40 miles, and a descent of 32 feet, falls 

 into 2. Lake Huron, having a length of 280 

 miles, and a breadth of 250 ; area 20,000 square 

 miles, and medium depth 1000 feet. It has 

 several large islands, among which are the Mani- 

 toulin chain, which almost separates that portion 

 known as Lake Iroquois or Georgian Bay from 

 the main body of the lake. 3. Michigan, on 

 nearly the same level with Huron, with which it 

 is connected by the Mackinaw Strait, little more 

 than four miles across. This sheet is 320 miles 

 long, and about 70 broad ; area 18,000 square 

 miles, and depth 1000 feet. The shores, which 

 are bold, and at certain seasons dangerous, are 

 guarded by 23 lighthouses. Along with the lower 

 lakes and the St Lawrence, it forms a natural out- 

 let for one of the richest grain-growing regions 

 in the world. 4. Lake Erie, receiving the surplus 

 waters of Huron by the navigable rivers St Clair 

 and Detroit the former, after a course of 30 

 miles, expanding into a shallow lake, which again 

 contracts into the latter, also about 30 miles long. 

 Erie is 240 miles long, and from 30 to 60 broad ; 

 area 9600 square miles ; its level 560 feet above 

 the sea, and mean depth 120 feet. The shores 

 of this sheet are low, with a marshy or sandy 

 beach. 5. Ontario, receiving the surplus waters 

 of Erie by the Niagara, has a descent of 330 feet, 

 165 of which are by the celebrated Falls of that 

 name. This lake is 190 miles long, and 55 at its 

 broadest ; area 7200 square miles, depth 500 feet. 

 Its shores are in general flat. The navigation 

 has been facilitated by a system of lighthouses on 

 both sides of the lake. Ontario discharges its 

 waters by the Lake of the Thousand Islands, 

 which afterwards becomes the St Lawrence. The 

 other principal lakes are Athabasca, Winnipeg, 

 Great Slave Lake, and Great Bear Lake in the 

 Hudson Bay Territory ; the Great Salt Lake in 

 Utah, and Nicaragua in Central America. 



With respect to rivers, no country is more 

 bountifully supplied than North America, almost 

 every part of its interior being accessible by their 

 means. The Mississippi reckoning from the 

 source of the Missouri, its true head has a course 

 of 4500 miles, for 3950 of which it is navigable 

 for boats. It has been calculated that the basin 

 of this river has an area of 1,220,000 square miles, 

 and that the whole amount of boat-navigation 

 afforded by the river-system, of which it is the 

 main trunk, is nearly 40,000 miles. It has 1500 

 navigable branches, of which the principal are the 

 Red River, Arkansas, Platte, and Yellowstone on 

 the west ; and the Tennessee, Ohio, Wabash, and 

 Illinois on the east. The St Lawrence, estimating 

 its course from the head-waters of the rivers 

 flowing into Lake Superior, drains a territory of 

 560,000 square miles, and affords a partially 

 interrupted boat-navigation of 4000 miles. The 

 other large rivers are the Mackenzie, nearly 1800 

 miles in length, and flowing through a succession 

 of lakes into the Arctic Ocean ; the Columbia or 

 Oregon, the largest river west of the Rocky Moun- 

 tains, but with a current so rapid and obstructed 



that it is of little value for inland navigation ; the 

 Bravo del Norte or Rio Grande, the boundary 

 j between Mexico and the United States, and next 

 I to the Mississippi the largest river flowing into 

 the Gulf of Mexico, being fully 1800 miles in 

 I length ; and the Colorado, which rises in the 

 Rocky Mountains, and after a broken and rapid 

 j course of 1200 miles, falls into the Pacific at the 

 i head of the Gulf of California. These, as well 

 i as many others of the minor rivers, exhibit in 

 their course some of the magnificent and pictur- 

 esque water-falls, of which Niagara (165 feet) and 

 Montmorency in Canada (250 feet), the Katerskill 

 (175), and Great Falls (150) in the United States, 

 ! may be taken as examples. 



GEOLOGY. 



The geology of the New World presents some 

 remarkable contrasts to that of the districts in the 

 Old World which have supplied the types of 

 geological classification. None of these is more 

 striking than the enormous extent of country 

 which one formation occupies, and that with- 

 out interruption. American strata often stretch 

 from the Atlantic west beyond the Mississippi. 

 They have, on the whole, been subject to few dis- 

 turbing agencies. It is not many years since 

 attention was first directed to American geology ; 

 but during the short time that has intervened, its 

 progress has been very remarkable. The oldest 

 strata are a range of crystalline rocks, which 

 occupy an area that extends from the northern 

 shores of Lake Superior and the banks of the St 

 Lawrence north-west to the Arctic Ocean, and 

 lies between the line of minor lakes and Hudson 

 Bay. The average width of this area is about 

 200 miles, and its length from Lake Superior to 

 its termination on the shores of the Arctic Sea is 

 more than 1500 miles. The rocks are chiefly 

 gneiss with granite and trap. They also form the 

 western slopes of the Rocky Mountains. On 

 either side of this tract there exists a Silurian dis- 

 trict. That on the eastern side, reaching to Hud- 

 son Bay, has a low and uniformly swampy aspect. 

 The other covers a large extent of the continent. 

 It bounds the southern limits of the azoic rocks 

 along the line of the great lakes, extending in 

 a broad band of some 200 miles, parallel to the 

 more ancient formation, till it nears the Arctic Sea. 

 These Silurians have been divided into Lower and 

 Upper, each of which contains three periods. 

 The Lower Silurian periods are the Potsdam, the 

 Trenton, and the Hudson, comprising beds of 

 slate, sandstone, limestone, clays, and shales, with 

 numerous fossil remains. The Upper Silurian 

 periods are the Medina-Clinton, the Niagara- 

 Onondaga, and the lower Helderberg, comprising 

 sandstone, shale, and limestone, also rich in fossil 

 remains. The Silurian beds on their southern 

 and western borders dip under the Devonian rocks, 

 which are developed to a large extent north of lat. 

 72 N. Vast beds of conglomerate overlie the 

 Devonian rocks, and form the basis of the carbon- 

 iferous strata. This formation covers large dis- 

 tricts in New Jersey and Pennsylvania, and in the 

 Ohio and Mississippi valleys, with an enormous 

 thickness of limestone, shale, and other beds. 

 Volcanic activity has long ceased in the Appa- 

 lachian range, but one can still trace its former 

 presence in the highly metamorphosed Silurian 



