parallel belts, which are, in order from the E. toward the W., as follows: 1st, the South Mountains, being the continuation of the New York Highlands and the equivalent of the Blue Ridge in Virginia; 2d, the Great Appalachian Valley; 3d, the Central Appalachian ridges; 4th, the subAlleghany Valley; 5th, the Alleghany Mountains. The southern division of the Appalachians exhibits marked peculiarities of structure. The main chain, known as the Blue Ridge, which borders the great valley on the E., bears off to the S. W., leaving a wider seaboard and rising to a great height. In the regions comprised between the Blue Ridge and the chain of the Iron, Smoky, and Unaka mountains is the culminating portion of the Appalachians. For 150 miles the mean elevation of the valley is more than 2000 feet, while the mountains rise in scores of summits to 6000 feet or more. To the W. is the Valley of the Tennessee, a portion of the great central valley already mentioned. Still farther to the W. is the plateau of Tennessee, known as the Cumberland Mountains. Such is the system of mountains which form the eastern side of the framework by which the central portion of the United States is embraced. Between these and the Rocky Mountains are no connected masses of mountain-ranges. A few short ranges skirt the S. shore of Lake Superior, and here and there appear isolated hill-ranges, notably in Missouri and Arkansas.

The Cordilleras belong to the great chain of mountains which borders the Pacific coast of North and South America. Entering the United States from Mexico, the system widens rapidly until along the line from San Francisco, by way of Salt Lake, to Fort Laramie, the mass of mountains has a width of 1000 miles. "The whole area," says Prof. Whitney, "embraced within the mountainous belt which is called the Cordilleras is but very little, if any, short of 1,000,000 sq. m.; hence it may with propriety be called the greatest physical feature of our territory." This enormous mass of a lozenge shape, the length of each side being approximately 600 miles, is formed by the Cascade Range and the Sierra Nevada on the two westerly faces, and by the Rocky Mountains, with the Big Horn, Wind River, and Bitter Root ranges, on the two easterly faces. The plateau thus enclosed has through its centre, E. and W., an elevation of 4000 to 5000 feet, falling off alike to the N. and to the S. This plateau is traversed by various ranges, of which the Wahsatch, extending N. and S. through nearly six degrees, is the most notable. Between the Wahsatch and the Rocky mountains runs the Uintah range, the only high and well-defined chain in the Cordilleras having an E. and W. trend. W. of the Wahsatch are numerous parallel ranges, generally long, narrow, and precipitous, running obliquely from the Sierra Nevada E. of N. to the Humboldt River, beyond which lies the volcanic plateau which covers a large portion of Eastern Oregon and Washington, of Northern Nevada, Northeastern California, and South-western Idaho. From the plateau W. of the Snake River rise the Blue Mountains. The highest part of the Sierra Nevada is near the parallel of 36° 30', where the peaks rise above 14,000 feet, the passes having an elevation of nearly 12,000. Farther to the N., where the Pacific R. R. crosses, the pass is only 7000 feet above the sea-level. W. of the Sierra Nevada and the Cascade Mountains, and not always to be distinguished from them, lie the Coast Ranges of California and Oregon.

Ricer Systems.-The river systems of the United States may be grouped sectionally into four grand divisions-the northern lake, the Atlantic, the Gulf, and the Pacific divisions. The first consists of innumerable streams, many of them very short, emptying into the great lakes from Superior to Ontario, with which may here, for convenience, be associated the streams emptying into the river St. Lawrence and those running N. into British America. Of the last by far the most important is the Red River of the North, which empties into Lake Winnipeg in Canada. The whole river system thus composed embraces 184,339 sq. m. of the territory of the United States, lying between the 71st and 104th degrees of lon. W. from Greenwich. The second division comprises all those streams which flow eastward or southward to the Atlantic. This division covers the total eastern side of the United States, extending from 47° 15' to 25° 15' in latitude, and covers an estimated area of 304,538 sq. m. The most important rivers of this division, which embraces more than one-third the population of the United States, are the Penobscot, Kennebec, Androscoggin, Merrimack, Connecticut, Hudson, Delaware, Susquehanna, Potomac, Rappahannock, James, Roanoke, Neuse, Cape Fear, Pedee, Santee, Edisto, Savannah, Ogeechee, Altamaha, Saltilla, and St. Johns. The third grand division embraces the Mississippi system, and also the rivers of Western Georgia, Western Florida, Alabama, Mississippi, Louisiana, and Texas, which empty

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into the Gulf of Mexico. The total area of this division is computed at 1,683,303 sq. m., of which 1,257,545 are drained by the Mississippi and its tributaries, the principal of which, with their several areas of drainage, are the Missouri (527,690), the Ohio (207,111), the Arkansas (184,742), and the Red (92,721). Other prominent tributaries are the Minnesota, Des Moines, Illinois, and Yazoo. Of the rivers in this division emptying directly into the Gulf, the most important are the Suwanee, Apalachicola, Mobile, Pearl, Sabine, Trinity, Brazos, Colorado (of Texas), Guadalupe, and Nueces, the Rio Grande del Norte forming for a considerable part of its course the south-western boundary of the United States. The fourth grand division embraces the Great Interior Basin, without outlet to the sea, between the Rocky Mountains and the Sierra Nevada (210,274 sq. m.), and the basins of the Columbia, the Klamath, the Sacramento and San Joaquin, and the Colorado, as well as the tracts drained by smaller streams flowing into the Pacific. The total area is 854,314 sq. m.

A notable peculiarity of all the streams draining the Cordilleras to the W. is want of navigability. The mighty Colorado is almost without importance for purposes of navigation; the Columbia has two portages by railroad before the Cascade Range is passed; the Sacramento is navigable for moderate-sized boats for only 60 miles. In striking contrast are the rivers of the Mississippi Valley, which offer vast reaches to steam navigation. Cairo is 1100 miles from the mouth of the Mississippi, yet only 322 feet above the level of the Gulf; Pittsburg, at the head of the Ohio, 975 miles farther from the sea, has an elevation of only 699 feet.

The Great Lakes.-The upper waters of the St. Lawrence River expand between the 76th and 92d degrees of lon. W. from Greenwich into a series of lakes, which form, for the greater part of that distance, the northern boundary of the United States. These lakes are five in number-Ontario, Erie, Huron, Michigan, and Superior. They are remarkable not alone for their immense area, but for their uniformity of elevation, affording extraordinary facilities for commercial intercourse. Lake Michigan is but 19 feet higher than Erie, while Superior is but 22 feet higher still. Between Erie and Ontario, however, there is a descent of not less than 331 feet, about one-half being made at a single plunge in the Falls of Niagara. These lakes have considerable depth, their basins being below the surface of the sea. Their combined area exceeds 90,000 sq. m., one-third being covered by the waters of Superior, while Michigan and Huron have each a surface of over 20,000.

Climate. To speak of the climate of the United States would be misleading. Nothing can be said of the United States as a whole in respect to temperature, humidity, or the force of winds. The United States, owing to its vast extent in latitude and to the influence of the great longitudinal chains of mountains, has many climates. The annual rainfall ranges from 72, 80, and even 100 inches upon the Upper Pacific slopes, to 12, 8, and even 4 inches only on the great interior basin between the Rocky Mountains and the Sierra Nevada. The mean annual temperature ranges from 72° or 76° F. in Southern Florida and portions of Arizona to 36° on the plains of Northern Minnesota and Dakota. (See each STATE and TERRITORY.)

Flora. The flora of the United States, as might be inferred from the wide range of soil, topography, geology, and climate, is both rich and varied. No full enumeration of plants has ever been published, but the whole number, exclusive of the lower cryptogams, probably amounts to 5000 indigenous species, many of which have a great range. There is perhaps not a single State which does not possess 1000 species; many States have 1500, while California has 2500 or 3000. The number of woody species is not less than 800, and over 400 are large enough to be called trees, 250 of which are not rare. If we consider only the larger and more important, excluding all the smaller and rarer ones, and also those tropical forms found only along the extreme southern border, there still remain about 120 species of trees within the United States in sufficient abundance to be somewhere of economic importance, which attain a maximum height of 100 or more feet. Twelve of these occur 200 feet high, and five or six are sometimes 300 or more feet. About 50 of the 120 species belong to the Coniferæ.

Compared with Europe, the local floras are poorer in the actual number of species, but vastly richer in trees, many of which belong to older types. The hickories, magnolias, sequoias, liquidamber, sassafras, and other genera, so abundant or noteworthy in the New World, are only found fossil in the Old.

The United States has contributed a few species to the useful plants of cultivation. Many valuable varieties of grasses have originated from native species, and several fruits and nuts now but rarely cultivated will probably

pass into wider cultivation and greater economic importance. Near the Atlantic coast and along our southern borders European explorers found maize, potatoes, squashes, tobacco, and other useful plants in cultivation among the Indians. Whether they were originally native, or had been introduced earlier from Mexico, cannot now be known. On the N. W. coast a poor kind of native tobacco was the only plant originally cultivated by the natives, and in the interior there were large regions where absolutely no plant was cultivated. The East has actually furnished a few useful plants to cultivation, and the West many ornamental species. In the gardens and parks of Europe it has been remarked that Asia has furnished the larger number of useful trees and shrubs (other than timber), and North America, particularly the United States, the most beautiful of the ornamental species.

Fauna. No account exists of the species of the animal kingdom within the limits of the United States. In general, the fauna is the same as that of North America, which is especially rich in fresh-water forms, for the reason, doubtless, that North America has been a continent ever since the Carboniferous period. The species of Vertebrata described number 2249, distributed as follows: Mammalia, 310; Aves, 756; Reptilia, 257; Batrachia, 101; Pisces, 816; Dermopteri, 8; Leptocardii, 1. The Mollusca found in rivers and lakes number 1034 species; about 400 more are terrestrial and air-breathers; the marine species are very numerous, but nothing approaching a complete enumeration is possible. Of the number of species in the inferior divisions of the animal kingdom only the rudest estimates can be made. Of insects, Prof. Cope considers 50,000 species as probably "below the mark."

Geology.-In describing the geology of the United States it will be convenient to divide the territory into two great geographical areas the eastern from the Atlantic to the base of the Rocky Mountains, and the western extending thence to the Pacific. The eastern is occupied in large part by an immense basin of Palæozoic rocks, bounded on the W. by the crystalline Eozoic formations of the Rocky Mountains; which formations, with some intervals of concealment, stretch around to Lake Superior, and thence through Canada to the mountainous regions of Northern New York and New England. They are thence prolonged south-westward in the Highlands of Southern New York, New Jersey, and Pennsylvania, and continued in the Blue Ridge as far as Alabama. Within the great basin thus enclosed on the N. and E. and W. lie the uncrystalline rocks of Paleozoic age, including representatives of all of the great divisions of Palæozoic time-Cambrian, Silurian, Devonian, and Carboniferous.

The geological structure of the great western area, including the region from the eastern base of the Rocky Mountains to the Pacific, differs widely from that of the eastern. The crystalline rocks of the Eozoic are in parts overlaid by Paleozoic strata, which, though holding the organic forms of those of the eastern basin, are unlike them lithologically, being in great measure limestones, of which a large portion are of Carboniferous age. Vast areas of more recent rocks, in great part of the newer Secondary and Tertiary periods, occur in these regions, including large deposits of coal and the remains of a great variety of vertebrate animals. These strata, which are undisturbed in the Atlantic and Gulf regions, have in the West been greatly broken and faulted and eroded, and penetrated by eruptive rocks, overflows of which cover wide territories in the north-western part of the area.

Over the north-eastern portions of the United States the strata already described are irregularly overlaid in parts by the so-called Drift formation, supposed to be the result of ice-action. The higher portions of the hard and often crystalline rocks are rounded and scratched or grooved, while in the lower levels is found the unstratified or glacial drift with boulders, overlaid by stratified clays and sands. These deposits are more recent than the Pliocene Tertiary. The southern limit of the Drift is about 40° N. lat.; beyond this the limestones and the crystalline Eozoic rocks are in great part covered with a soil resulting from their decay in place. This decayed covering is seen at intervals, where the strata have been protected from glacial action, as far N. as Massachusetts, but is remarkable in the Blue Ridge, where the hard crystalline rocks are often concealed beneath a layer of 100 feet or more of softened material, resulting from the decomposition of these in situ. Similar phenomena are seen in the upper valley of the Mississippi, which, like the S., has escaped the agencies of the Glacial period.

Iron. The iron resources of the United States are stupendous in extent. All varieties of ore are found, most of them in great abundance, and in such juxtaposition with coal and limestone, often close upon navigable waters, as to afford the highest facility for production. Magnetic

ores are found in the Adirondacks and throughout the entire length of the Alleghanies. They have been developed especially in the Champlain district about Port Henry, in Orange co., N. Y., in Northern New Jersey, and in Lebanon and York cos., Pa. These ores are largely used in the manufacture of Bessemer steel. Magnetic ores, as yet undeveloped, are also found in the Black Hills and various parts of the Rocky Mountains and the Sierra Nevada. In the Lake Superior region, and in the region of Central Missouri, where are literally mountains of iron, occur vast deposits of hæmatite ores, the production of the Lake Superior region reaching nearly 1,000,000 tons a year, the product being widely distributed, like the magnetic ores of the East, both by boat and by rail, to hundreds of furnaces, some at a great distance. Red hæmatite ores are found over broad areas from Maine to Georgia and East Tennessee, the variety known as the Clinton or fossil ore being of unsurpassed industrial importance, though not used in the manufacture of steel. Brown hæmatite or limonite ore occurs on both sides of the Alleghanies, and also in Missouri. This ore is adapted for use as an adjunct to the magnetic ores, and at the East the two are generally worked together. Spathic iron (the sparry carbonate of iron) is found only in two deposits of economic value in the United States, in Roxbury, Conn., and near Burlington, Vt. The earthy carbonate (clay ironstone) is found plentifully throughout the Alleghany coal-field, and occurs also in Illinois and Missouri. This variety is less used than formerly, when it supplied large numbers of furnaces in Pennsylvania and Ohio, especially in Western Pennsylvania and Southern Ohio. Another carbonate of iron, blackband ore, the chief material of the Scotch iron manufacture, has been found in 'considerable amount in Ohio, and in small quantities in the anthracite region of Pennsylvania. (See IRON.)

Coal. The extensive coal-measures of the United States may be grouped into seven grand divisions: the New England basin, the anthracite regions of Pennsylvania, the Appalachian coal-field, the Michigan, the Illinois, and the Missouri basins, and the Texas coal-field. The New England basin in Massachusetts and Rhode Island occupies about 750 sq. m.; the coal is a plumbaginous anthracite. Small quantities are raised for use in smelting. The anthracite basins of Pennsylvania are estimated to embrace 472 sq. m. They are usually divided into three groupsthe first, the southern, or Schuylkill basin and Mine Hill; the second, the middle, or Shamokin, the Mahanoy, and the Lehigh basins; the third, the northern, or Wyoming and Lackawanna basin. Prof. Rogers reports that the first coal-field has an average thickness of 100 feet, the second and third of about 60 feet. The Appalachian coal-fields comprise over 59,000 sq. m., distributed as follows: Pennsylvania, 12,302; Maryland, 558; Ohio, 10,000; Virginia and West Virginia, 16,000; Kentucky, 8983; Tennessee, 5100; Georgia, 170; Alabama, 6000. The Michigan basin has an area of 6700 sq. m., with 123 feet of measures and 11 feet of coal as a maximum in the centre of the basin. The coal-measures of the Illinois basin occupy about 47,188 sq. m. in the States of Illinois, Indiana, and Kentucky. In this field the beds of coal are not so thick as in the Appalachian, though their number is about the same. The coals themselves are more apt to be impure, though there is abundance of good workable beds. In Illinois the measures occupy 36,000 sq. m. In Indiana the measures occupy 6500 sq. m. In Western Kentucky this field occupies 3888 sq. m. The Missouri basin covers the largest expanse of territory, though it is thinner and with fewer beds of coal than the Appalachian. In this basin are embraced 18,000 sq. m. in Iowa; 23,100 in Missouri; 36,000 in Nebraska; 17,000 in Kansas; 13,600 in the Indian Territory; and 9000 in Arkansas; a total of 84,300 sq. m. The Texas basin embraces about 6000 sq. m. (See COAL.)

In addition to all the above, there are considerable areas in the Rocky Mountains, underlaid with beds of lignite.

The Precious Metals.-The Appalachians in their southern parts present a somewhat remarkable variety of mineral deposits. Gold in greater or less quantity is found in nearly all the Southern States which share in the elevation of this chain. In North Carolina and Georgia mines have been worked from an early period, but with varying success. In 1849 the discovery of gold in California led to the development not only of a new industry, but of a new empire. In two years the population of the Pacific slope rose from 15,000 to 100,000, and now exceeds 750,000. The first form of gold-mining on the Pacific was that of diggings, the soil being shovelled into a pan, and the gold washed free of the clay, sand, and pebbles. Later came the rocker, afterward the "tom" and the sluice. The first ditch of importance was made in 1850, while in the eight years following 6000 miles of mining-canals had been con