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RIVERS are to be traced to springs, or to the gradual meltings of the ice and snow which perpetually cover the summits of all the most elevated ranges of mountains upon the globe. The union of various springs, or of these meltings, forms rivulets: these last follow the declivity of the ground, and commonly fall, at different stages, into one great channel, called a river, which, at last, discharges its waters into the sea, or some great inland lake. The declivities along which descend the various streams that flow into one particular river are called its basina term, therefore, which includes the whole extent of country from which the waters of the river are chawn. As mountainous regions abound in springs, we find that most RIVERS, more especially those of the first class, commence from a chain of mountains; each side of a chain also has its springs, and the rivers which originate on one side flow in the opposite direction to those which rise en the other. As it is the property of water to follow the most rapid descent that comes in its way, the courses of streams point out the various declivities of the earth's surface, and the line from which large rivers flow in contrary directions (German Was'serscheide), generally marks the highest parts of the earth. In European Russia, where the rivers are very extensive, there is, however, a singular exception to this rule, the line which separates the sources of those rivers being veiy little above the level of the Baltic, or of the Black sea. It has been observed, by some writers, that the extent of a river is in proportion to the height of the range of mountains from which it descends. This is, in a certain degree, true, because the greater the bulk of the mountains, the more numerous the springs and torrents which they furnish; but the relation between the extent of a river and the surface of its basin is much closer and more invariable. Even this is not sufficiently comprehensive; for it is evident that the size of a river depends upon three circumstancesthe surface of its basin; the abundance, or otherwise, of that surface in springs; and the degree of humidity possessed by the climate of the region from which it draws its supplies. As many springs, however, are formed by the rains, the second of these circumstances will, in some measure, vary with the last. By an attention to these remarks, the causes of the great size of the South American rivers will be apparent. The peculiar position of the Andes, with respect to the plain of that continent; the fact, that by very far the largest proportion of its running waters are drained off in one general direction (towards the Atlantic); the multiplicity of streams that intersect the country; and the humidity of the climateall contribute to that result. The Andes being placed so near the coast of the Pacific, the rivers which flow from them into that ocean are small; wlnle those which flow on the other side, having such an immense space to traverse, are swelled into a most majestic volume before they reach the Atlantic. The physical circumstances of the old continent are unfavorable to the accumulation of such vast bodies of water as the rivers of South America. Europe is not of sufficient extent; Africa is oppressed by a scorching climate, and abounds in sandy deserts ; in Asia, the atmosphere generally is not so moist, while the more central position, for the most part, of the great mountainous range of that continent, and the existence of capacious inland lakes, which are the final receptacles of the streams that fall into them, are the causes why the waters are more equally drained off in different directions than in the NewWorld. When water, by following a descent, has once received an impulse, the pressure of the particles behind upon those before will be sufficient to keep the stream in motion, even when there is no longer a declivity in the ground. The only effect is, that in passing along a level, the course of the stream becomes gradually slower an effect which may be perceived, more or less, in all running waters that originate in mountainous or hilly tracts, and afterwards traverse the plains. The declivity of many great rivers is much less than might at first be supposed. The Maranon, or Amazons, has a descent of only ten and a half feet in 200 leagues of its course, that is, one twentyseventh part of an inch for every thousand feet of that distance. The Loire, in France, between Pouilly and Briare, falls one foot in 7500 but between Briare and Orleans, only one foot in 13,596. Even the rapid Rhine has not a descent of more than four feet in a mile, between Schaffhausen and Strasburg, and of two feet between the latter place and Schenckenschantz. When rivers flow through a mountainous and rugged country, they frequently fall over precipices, and form cataracts (q. v.), in some cases, several hundred feet in depth. The most celebrated falls in the world are those of the Niagara, in North America, In the tropical regions, most of the rivers are subject to periodical overflowings of their banks, in consequence of the rains which annually fall in such abundance, in those countries, during the wet season. The overflow of the Nile was considered oy the ancients, who were ignorant of its cause, as one of the greatest mysteries of nature; because, in Egypt, where the overflow takes place, no rain ever falls. The apparent mystery is easily explained, by the circumstance of the rains descending upon the mountains in the interior of Africa, where the Nile rises. The consequent accumulation of the waters among the high grounds, gradually swells the river along its whole extent, and, in about two months from the commencement of the rains, occasions those yearly inundations, without which Egypt would be no better than a desert. The disappearance of some rivers, for a certain distance, under ground, is accounted for with equal facility. When a river is impeded in its course by a bank of solid rock, and finds beneath it a bed of a softer soil, the waters wear away the latter, and thus make for themselves a subterraneous passage. In this way are explained the sinking of the Rhone, between Seyssel and L'Ecluse, and the formation, in Virginia, of the magnificent rock bridge which overhangs the course of the Cedar creek. In Spain, the phenomenon exhibited by the Guadiana, which has its waters dispersed in sandy and marshy grounds, whence they afterwards emerge in greater abundance, is to be referred to the absorbing power of the soil. Bivers, in their junction with the sea, present several appearances worthy of notice. The opposition which takes place between the tide and their own currents, occasions, in many instances, the collection at their mouths of banks of sand or mud, called bars, on account of the obstruction which they offer to navigation. Some streams rush with such force into the sea, that it is possible, for some distance, to distinguish their waters from those of the sea. The shock arising from the collision of the current of the majestic Amazons with the tide of the Atlantic is of the most tremendous description. (See Mascaret.) Many of the largest rivers mingle with the sea by means of a single outlet, while others (for instance, the Nile, the Ganges, the Volga, the Rhine, and the Orinoco), before their termination, divide into several branches.* This circumstance will depend upon the nature of the soil of the country through which a river runs; but it also frequently* The triangular space formed by a river pouring itself into the sea by various mouths, is called a Delta, from its resemblance to the shape of the fourth letter (A) of the Greek alphabet. results from the velocity of the stream being so much diminished in its latter stage, that even a slight obstacle in the ground has power to change its course, and a number of channels are thus produced. Another cause may be assigned for the division into branches of those rivers which, in tropical countries, periodically inundate the plains ; the superfluous waters which, at those periods, spread over the country, find various outlets, which are afterwards rendered permanent by the deepening of the channels by each successive flood. In some of the sandy plains of the torrid zone, the rivers divide into branches, and, from the nature of the soil and the heat of the climate, they are absorbed and evaporated, and thus never reach the sea. (See the articles Amazons, Plata, Mississippi, Missouri, Laivrence, St., Danube, Rhine, Nile, Niger, Ganges, &c.) Rivers, Navigable, form one of the most important items of the productive capacity of a country; and a view of the navigable rivers of all the different countries, taken from good authorities, would be a most interesting document for the political economist, but would much exceed the limits of the present wrork; so that we are obliged to confine ourselves to a brief sketch of the navigable rivers of North America. The canals have been treated of under the heads of Canal, and Inland Navigation. (For the rivers of other countries, see the respective articles.) The most natural way of treating the subject would be according to the basins of the largest rivers. Mr. Darby, in his View of the United States (Philadelphia, 1828), gives an interesting account of these basins. North America empties its waters into the sea, through many rivers, the largest of which, on the eastern side, are the Mississippi and St. Lawrence ; on the western, the Columbia or Oregon ; and on the northern, Mackenzie's RIVER. (For further information respecting the origin of these rivers, their connexion with others, and with lakes, see our article North America; for the Mississippi and its navigation, see Mississippi.) Its principal tributary stream is the Missouri, (q. v.) Owing to the secondary character of the country, the numerous branches of these rivers are generally navigable, and afford a passage from almost every part of the Western States and the vast regions at the base of the Rocky mountains (q. v.) to the gulf of Mexico and the ocean, at least during the season of high water, from the spring to the middle of summer. The current of the principal rivers is so rapid, navigation is chiefly carried on by means of steamboats. The Arkansas river is the next branch to the Missouri in size. (See end of the article Arkansas.) The Canadian, a branch of the Arkansas, 1000 miles in length, is navigable 100 miles. The Red river is navigable 500 miles from its junction with the Mississippi. (See Red River.) The tributaries of the Missouri are usually blocked up at their mouths, afte* the floods in July, until the next spring, with mud brought down by the Missouri. The Platte (q. v.) is fordable in almost every part, and navigable only for canoes made of skins. The Yellowstone (q. v..) is navigable through the greater part of its course. Other important branches of the Missouri are the Kansas (q. v.) and Osage (q. v.), navigable for boats 600 miles. The chief branches of the Mississippi above the Missouri are the Illinois (q. v.), River de Moines, Rock river, St. Peter's, and Wisconsin, each of which may be considered as affording 400 to 500 miles of navigation. The White river, 1300 miles long, joins the Mississippi 51 miles above the Arkansas, and is said to be navigable for boats 1200 miles. On the eastern side, the largest branch of the Mississippi is the Ohio, (q.v.) Its branches are the Alleghany (q. v.), Mo nongahela(q. v.), Muskingum, Scioto(q.v.), Big Beaver, Hockhoching (q. v.), Great Miami (q. v.), Wabash (q. v.), Great Kenhawa (q. v.), Big Sandy, Kentucky (q. v.), Green river (q. v.), Cumberland (q. v.), and Tennesee. (q. v.) They are all navigable for several hundred miles. Among the rivers emptying into the gulf of Mexico, are also the Appalachicola (q.v.), in Florida; Mobile (q. v.), formed by the junction of the Alabama (q. v.) and Tombigbee. (q. v.) The Cahawba falls into the Mobile. All are navigable for a considerable extent. Between Mobile bay and New Orleans, there is an interesting inland navigation through lake Ponchartrain (q. v.), the Rigolets, lake Borgne (q. v.), Pass au Chretien, and Pass au Heron. This is formed by a chain of islands, and is not navigable for vessels drawing more than five feet. Pearl river joins the Rigolets. Its navigation is much impeded by shallows and timber. Sabine river, forming the eastern boundary of Texas, is navigable about 280 miles, but has only three feet water on the bar at its mouth. The Atchafalaya, Teche and Courte, unite to form a river of great importance west of the Mississippi. It flows into the bay of Atcha sissippi, admits vessels drawing four to five feet to within thirty miles of its efflux(For the Rio del Norte, see Norte, Rio del.) The Rio Huasaculco and Alvarado, both southeast of Vera Cruz, are calculated to facilitate the communication with Guatimala. The St. Jago might form a communication to Port St. Bias or the Pacific. The river Atrato, which falls into the gulf of Darien, southeast of Panama, is united by a little canal, for boats in the rainy season, with Rio San Juan, a brook which empties into the Pacific. The Colorado, about 1000 miles long, empties into the gulf of California. (For lake Nicaragua, 120 miles long, 41 wide, see Nicaragua.) The Columbia or Oregon has three great tributaries, the Multnomah (q. v.), Lewis's river (q. v.), and Clarke's river. Vessels of 300 tons may ascend to the mouth of the Multnomah, 125 miles, and sloops to the head of tide water, 60 miles farther. (For more information respecting this river, see the article on it: for Mackenzie's river, see the article.) Coppermine river is scarcely navigable by canoes near its opening into the Polar sea. Churchill river, which empties into Hudson's bay, but is connected by means of lakes with the river Athapescow, would form an invaluable communication, were the climate less rigorous. The Saskashawin is formed by two considerable rivers that come from the foot of the western mountains, and falls into lake Winipeg. (q. v.) This lake receives the great river Assiniboins (q. v.), from the south side after the junction of that sfream with Red river, and discharges itself into Hudson's bay by the Nelson and Severn rivers. (For the St. Lawrence, see Lawrence, St.) This river affords, even in winter, means of easy communication by sledges. The common route of fur traders, in their bark canoes, is from the St. Lawrence, through the Ottawa or Grand river, and thence by a short portage to lake Nipissing, and down the French river into lake Huron. From lake Huron they proceed, through the straits of St. Mary and lake Superior, to the Grand Portage, nine miles in length, which brings them to the great northern chain of lakes, beginning with the lake of the Woods, at the distance of 1100 miles from the place of their departure. Ottawa river flows into the St. Lawrence above Montreal. Its course is interrupted by rapids and falls; but fur traders overcome these difficulties with their canoes. St, John's flows through New Brunswick, and runs into the bay of Fundy. For boats it is navigable 200 miles ; for sloops of fifty tons, 80 miles. Its tributaries are the St. Francis (q. v.), Aroostook, Madawaska. As a navigable channel, it is ?superior to any northeast of the Hudson. The numerous rivers on the eastern declivity of the Apalachian chain afford the advantages of a good inland navigation to most parts of the Atlantic states. In all those streams which flow through the alluvial region from the Mississippi to the Roanoke, the tide waters of the ocean terminate at some distance from the foot of the mountains, varying from 30 to 120 miles. From the Roanoke to the Hudson, they extend through the alluvial region to the base of the primitive hills; but in no rivers south of the Hudson do they pass beyond the alluvial region. As far as the tide flows, the streams are generally navigable for sloops. In passing from the hilly and primitive to the flat and alluvial region, the streams are almost uniformly precipitated over ledges of rocks, by rapids, which obstruct their navigation. Indeed, the line of alluvion marks the line of navigation from the sea, which passes through Milledgeville on the Altamaha, Augusta on the Savannah, Columbia and Camden on the Santee, Richmond on the James, Fredericksburg on the Rappahannock, Georgetown on the Potomac, and Trenton on the Delaware. (See the articles on these rivers, and our article North America, division Geology of.) Above the rapids, navigation is performed entirely by boats propelled by oars or poles, or drawn up by ropes, or by means of the bushes growing on their banks. (For the Savannah river, see the article.) The rivers of South Carolina are navigable nearly through the alluvial region, and there are some good harbors at their mouths. The coast of North Carolina is bordered with a range of low, sandy islands, enclosing a chain of sounds. Their entrances are generally obstructed by bars, which vessels of considerable size cannot pass. Rut the streams are navigable for sloops some distance into the interior. The Chesapeake bay is, of itself, an inland sea of considerable size, and, with the numerous streams and inlets on its borders, forms an important channel to the ocean for a large extent of country, including the whole of Maryland and the eastern declivity of Virginia, and extending through the middle section of Pennsylvania, nearly to the small lakes of New York. (See Chesapeake, James River, Potomac, Susquehannah. For the Delaware bay and river, see Delaivare.j New Jersey has the Rari* tan (q. v.); and the Passaic (q. v.) and Hackinsack afford a short inland navigation. The Hudson is the only river in the II. States where the tide passes through the alluvial, primitive and transition formations. It is navigable for ships to the city of Hudson, and sloops of considerable burden pass through all the formations, to the falls of the secondary country, above Troy, which is 165 miles from the ocean. (See Hudson.) In the rivers of the U. States east of the Hudson, the tide extends only a small distance, and the navigation is obstructed by the falls and rapids, which are common in primitive countries. The Connecticut is navigable for vessels of considerable size fifty miles, to Hartford. (See Connecticut.) The Merrimac (q. v.) of New Hampshire is much obstructed by rapids. The rivers of Maine are generally obstructed. The Penobscot (q. v.), the St. John's, already mentioned, and the western branch of the Kennebec (q. v.), afford a boat navigation nearly to their sources. The heads of these rivers approach within no great distance of the waters of the St. Lawrence ; and the portage from the head of the Kennebec to that of Chaudiere river is only five miles. The waters of the St. Lawrence or the great lakes have two natural communications with the branches of the Mississippi at particular seasons. The Fox river, which flows into the branch of lake Michigan called Green Bay, rises near the Wisconsin branch of the Mississippi, and afterwards flows within a mile and a half of its channel, separated from it only by a short portage over a prairie.