good harbors on the Atlantic coast than on the Pacific or Gulf coasts.

Topography. The main part of the United States presents four physical divisions: two elevated and two lowland regions. The elevated are the Appalachian Mountains (q.v.) in the east, and the Rocky Mountains (q.v.) or Cordillerian system in the west. The eastern lowland mass is along the Atlantic coast, broad at the Gulf of Mexico and narrowing towards the north where the mountains are but a short distance from the ocean. The southern part of the Atlantic lowland joins the central lowland region south of the Appalachian Mountains, and about 70 miles from the Gulf of Mexico. It is much less in extent than the central lowland division but it contains a large population, is the oldest portion settled by Europeans and was the chief battle ground in the war for American independence. The northern and southern parts of this lowland section differ materially in formation and soil. The mountains in the northern part approach the ocean so that the foot-hills are almost at the sea line; the lowlands are in some places really series of low hills, masses of rocks, sandy soil, large areas covered deep with glacial deposits, and with masses of rock formation which show the marks of mighty ice-forces. Beginning with and including the southern portions of New Jersey, and continuing to the Gulf and Florida Strait, is a plain of low, almost level, land, extending in a gradual slope from the mountains to tide water. The soil and climate contribute to the extensive growth of fruits, tobacco, corn, and cotton. The northern section of the Atlantic lowland is a worn-down mountain region, and the southern section at no ancient period was sea-bottom and even now the line of demarcation between the coastal plain and the continental shelf is very slight in many places. This section has received the name of "Tide Water Country," on account of its being a gift to the continent from the sea, and also because many of its rivers are tidal streams for some distance from the ocean. The central lowland lies between and on the lower slopes of the two great uplifts. It is called the Mississippi Valley on account of the greater portion being in the basin of the Mississippi River. higher slopes, merging into the foot-hill region of the Appalachian on the east and the Pacific on the west, become the plateau lands. The large grassy, almost treeless areas in this section are called prairies. This great lowland region of the United States is a part of the central lowland section of North America, which is called, in Canada, the Hudson Bay and Mackenzie regions. In the southern part of this section are vast areas of flood plains, and also land which at no very remote period was wholly under water. Beginning with the Atlantic plain or lowland at Florida, extending west and including the southern part of the central lowland section, there are broad areas only a few feet above sealevel, in many places less than 100 feet. The northern part of this central section is bounded by the Great Lakes. The divide between the streams that flow into the Great Lakes and those which flow into the Gulf of Mexico, by way of the Mississippi, is very slight. The three long slopes in this division are the one from the northern part to the Gulf; the one from the Appalachian divide on the east to the Mississippi; and the third from the Rocky

The

Mountain divide on the west to the Mississippi. There are numerous sand bars and swamp lands along the southern coast. The eastern slope is shorter and less steep as a whole than the western slope. There are high bluffs along many of the rivers of the western part, even in sections where there are large areas of rolling prairie lands. The huge boulders and mountain peaks of the northwest section seem like outposts on the beginning of the plateau region. In the southwest the lowlands extend around the southern part of many of the mountain chains, so that the greater part of the United States south of the low rocky hills which form the extremity of the Appalachian Mountains, and extending west to the Guadalupe Mountains, is one continuous lowland mass. The mountains in Missouri and Arkansas, south of the Missouri River and just west of the Mississippi, are the most important highlands in this whole section. In Missouri these highlands are called Ozark Mountains or Ozark Plateau, in Arkansas Ouachita Mountains.

Along the Pacific coast is a narrow strip of low land of not sufficient extent to be classed among the great physical divisions, but of great value from an economic point of view. The southern part of this lowland border is considerably wider than that of the northern part. The numerous parallel valleys, in some places valley arms, which are on the eastern border of the Pacific lowland strip, furnish a considerable area of productive farm lands.

The eastern uplift, the Appalachian Mountains, are the older and less extensive of the two great highland sections of the United States. (See APPALACHIAN MOUNTAINS.) They consist chiefly of mountain ranges which are nearly parallel with the Atlantic coast, and extend from near the Gulf of Mexico north into Canada. Nearly all of the western part of the United States, beginning about the 104th meridian, belongs to the Rocky Mountain region. (See ROCKY MOUNTAINS.) This portion of the United States has a greater altitude and extent than the mountain lands of the Atlantic region. The Rocky Mountains extend from Mexico to Canada. The ranges which constitute this group are by no means as regular in arrangement as are the Appalachian chains; some extend nearly parallel with the coast; many lofty ranges are at almost right angles with the north and south ranges, and others run northeast and southwest. Enclosed by ranges of these mountains are the Great Basin (q.v.) and the Yellowstone Park (q.v.). The Great Basin region is a series of basins isolated to all appearances from each other so far as drainage lines, and differing in soil and geological formation. The chief basins are the Carson, Humboldt, and Great Salt Lake. The mountain ranges within the Great Basin trend mostly north and south. The vast area of the volcanic region of the Rocky Mountains contains many extinct volcanoes. On both the eastern and western border are numerous high peaks connected by high plateaus. In the southern part or the portion drained by the Colorado River, is a region of high plateaus crossed by streams which flow through deep cañons, some of which are over 2,000 feet deep. The Grand Cañon (q.v.) of the Colorado is in places 6,000 feet deep.

Hydrography-The great streams which constitute the drainage systems of the United

States flow into the Atlantic, direct or through the Gulf of Mexico, and into the Pacific. The large river systems are the Mississippi, the Saint Lawrence, the Columbia, and the Colorado. The Mississippi (q.v.) is the largest, including within its basin nearly all the region in the central lowland section, and a large area of the Rocky and Appalachian mountains. The chief tributary is the Missouri (q.v.) which has a drainage area of about 530,000 square miles. Next in drainage area is the Ohio River (q.v.), the basin of which is over 200,000 square miles; the Arkansas, 185,671 square miles; the Red River, nearly 90,000 square miles. The total area drained by the Mississippi, its tributaries, and other streams which enter the Gulf, is 1,726,000 square miles. The Rio Grande, which also enters the Gulf of Mexico, has one large tributary, the Pecos. Further streams which flow into the Gulf of Mexico are the small Colorado, the Brazos, and others in Texas, and several rivers in Mississippi, Alabama, and Georgia. The Mississippi and its tributaries are navigable for thousands of miles. To the great central waterways is due the early development of the interior of the United States, first as a section with trading posts and forts at convenient places on the navigable streams, and later as a farming and manufacturing region. West of the divide in the Rocky Mountains the drainage is to the Pacific Ocean. Nearly all the rivers, except those in the Great Basin, flow directly,_or through a main stream to the open sea. The Colorado River enters the Pacific Ocean through the Gulf of California. The largest river of the Pacific basin is the Columbia (q.v.). Some of the other important rivers are the Sacramento, San Joaquin, Klamath, and a number of short streams. The rivers in California and some of the other valleys follow the course of the valleys, but the Columbia, Colorado, and branches of the Columbia break through the mountains in several places, and thus form high waterfalls and series of cascades. The Columbia has several large tributaries, chief of which is the Snake River (q.v.). The rivers of the Atlantic basin east of the Appalachians have mostly rapid currents, and have had great influence in the development of the manufacturing industries of the country. Many of the streams which flow into the Atlantic, or into wide bays which are arms of the ocean, are tidal streams for some distance inland. (See DELAWARE; HUDSON, etc.) The principal rivers of this basin are the Kennebec, Penobscot, and Manchester in the northeast; the Connecticut, which flows into Long Island Sound; the Hudson, a magnificent stream, alike remarkable for its scenery and its navigable importance, which flows south for 300 miles and contributes to form the harbor of New York; the Delaware, which after a course of 300 miles enters the Delaware Bay and is navigable for large steamers to Philadelphia, a distance of 4c miles; the Potomac, which flows into Chesapeake Bay, and is navigable for the largest vessels to Washington, a distance, including the bay, of 200 miles; and the Savannah, which enters Savannah Bay and is navigable for large vessels for 17 miles, to the city of Savannah, where it forms an important harbor. Besides the rivers, one of the most remarkable features of the United States, as also of Canada, is the chain of large fresh water lakes: Superior, Michigan, Huron, Erie, and Ontario. The

lakes drain an area of about 90,000 square miles, and send their waters into the Saint Lawrence, after precipitating the greater part of them in an accumulated mass over the renowned Falls of Niagara (q.v.), which are between Erie and Ontario. The rivers of the United States which flow into the Great Lakes (q.v.) are of no great length. The chief streams are the rivers of northern New York and Vermont, some of which enter the Saint Lawrence River through Lake Champlain; the Genesee River in the west central part of New York, and a number of small streams which enter Lakes Erie, Huron, Michigan, and Superior. (See SAINT LAWRENCE RIVER.) The Red River of the North enters the Atlantic Ocean through Lake Winnipeg and the Hudson Bay. In the interior of the United States are many groups of small lakes which have been mentioned in articles on the different States and Territories. The inland seas or salt-water lakes within the Great Basin are of special interest as being the remnants of large inland seas. The fresh-water lakes in the Appalachian section, and even the Great Lakes, were once much larger than at present. The chief characteristics of the whole drainage system of the United States are that by far the greatest portion of the waters are carried south or in a southern direction, and reach the Atlantic Ocean through the Gulf of Mexico. The Great Lakes with their large outlet, the Saint Lawrence River, receive but a small portion of the drainage; their chief supply comes from the melting snows of the Rocky Mountains. The rivers which enter the Pacific are small streams, except the Columbia and Colorado. The Red River of the North is the largest stream which flows north.

Geology. In the northeastern portion of the United States metamorphic, Devonian, and igneous rock prevail. Old sandstone, or middle Devonian is found along the shores of the Great Lakes. Older Paleozoic groups are found in Ohio, Wisconsin, Tennessee, and in many parts of the Appalachian region. Along the Rocky Mountains, extending north and south, is a wide belt of cretaceous formations. Tertiary formations prevail in the basin sections of the Rockies; igneous rocks are in the northwest and metamorphic strata along the Sierras. From the Rio Grande almost to the Hudson, the Tertiary formation is prominent. The oldest rock systems, the Archæan and Algonkin are found among the Appalachians. They consist of hard, crystalline rocks, granites, marbles, gneisses. schists, etc. The same formations, igneous and metamorphic, are found in Wisconsin, Minnesota, and portions of the Dakotas. The western part of the United States is much younger than the eastern part. (See Geology in articles on the different States and Territories.)

Mineralogy-Coal is mined in 28 States and a large area of unmined coal deposits is in the Rocky Mountains and Alaska. The anthracite coal is found in the eastern part of Pennsylvania and bituminous coal, varying in grade and value, in many other parts of the United States. East of the Rocky Mountains the total area of coal fields is about 222,000 square miles. Wood was the great fuel article of commerce in the eastern part of the United States until about the middle of the 19th century. Bituminous coal was used to some extent as early as the middle of the 18th century, but