There are some rivers which are entirely independent of tributaries—which pursue their way to the sea entirely alone. Such rivers, however, never belong to the first class; they are always of subordinate magnitude, and the humblest of them are mere coast torrents, like those west of the Andes. Others find their way to no ocean, but lose themselves in an inland sea or lake, as the Volga does in the Caspian; as the Gihon and the Sihon do in the Aral; as the Jordan does in the Dead Sea. Others disappear in sand wastes or in morasses; such are the rivers of the African steppes. Others are blocked up, as it were, by the tidal wave of the ocean, and are thus converted into estuary lakes.
There are some rivers, also, which remain equally or nearly equally full the whole year through; there are others which have their seasons of overflow: the Nile, for instance, and many rivers whose basin lies within the region of tropical rains; there are temporary rivers, now full, now empty, which, if they do not leave, like the torrents of Arabia, a perfectly dry bed, are traced in the dry season by a row of stagnant lakes, such, for example, as are found in the swampy lands of Australia.
What is peculiar to every river is determined by the abundance of its sources, the forking of its tributaries, the rate of its descent, the distance from its most remote springs to its mouth, the main direction of its course, and the greater or less sinuosities of its channel, as occasioned by the structure of the country which it traverses.
The abundance of its waters is conditioned by the greater or less amount of snow which finds the highest springs, the heavy rains which it receives in tropical countries, and the exceedingly varied influences which temperate climates may exert upon it. The fall softens from the rush and plunge of the mountain district, first to an arrowy swiftness, then to a moderate course, then to a beautiful gliding motion, to end with an almost imperceptible flow just before entering the sea.
The direction of rivers is determined:—
1. By the structure of the region which they traverse, the layers being in some places horizontal, and in others tilted to a vertical position; here grouped, as in the granite Carpathian chain, in such a way that the river courses which begin there run in parallel lines, radiating like the rays of a star from a central point; then grouped in such a manner that a stream may receive tributaries from two nearly contiguous ranges, as among the spurs of the Ural Mountains, the Rhone in Valais, receiving waters from the Bernese Alps at the north, and Pennine Alps at the south; the Isère, in like manner, the Upper Rhine in Grisons, the whole Upper Inn in Tyrol.
2. The direction is also determined by the mutual action of tributaries and the main stream at the point of confluence. Very often the union of two powerful currentsgives rise to a third direction, according to the law known as the parallelogram of the forces. This generally occurs when no obstacle stands in the way of their taking a normal course, and is exemplified in the cases of the Kama and Volga, the Theiss and Danube, the Rhine and Main, the Saone and Rhone. Where an obstacle stands in the way, their abnormal direction is manifested in the abrupt bendings of the river bed. An instance is found in the bending of the Rhone northward as it emerges from Valais. Its lower course, from Lake Geneva to Lyons, betrays the same angularities, resulting from the obstacles which it meets and cannot remove. The Rhine, breaking through the Jura at Basel, is another instance; the Rhine, between Bingen and Caub, and the Dal-Elf, in Sweden, also exemplify the same.
In case that rivers meet in their course large masses of stratified rocks, they force their way through them in a zigzag direction, making sharp angles always, and not unfrequently right angles, even. Instances of this are found in the Rhine, between Mayence and Coblentz, and in the Moselle, between Treves and Coblentz. When the river passes beyond these rocky barriers, and meets with obstructions of a more movable character, it crowds them more gently and gracefully aside, and leaves a path more sinuous and wave-like; and yet more gentle are its curves, as it opens a way through the plains where nothing obstructs its course. The last is strikingly exemplified in the rivers of eastern Europe, especially in all those of middle and southern Russia. The practised eye can determine the structure of the soil with considerable certainty, by merely tracing the course of rivers when represented on a faithful map. For, unless there be other reasons to prevent, rivers always force their way wherethere is the least resistance to overcome. In stratified rocks, where the tilt is so great as to make the strata vertical, the river beds usually run parallel with the lines of stratification. Instances are found among the Alpine rocks, in Valais along the Rhone, in Tyrol along the Inn and Adige, in Grisons, and among the Jura along the Rhine. Where the lines of stratification are horizontal, rivers usually take their course through the most marked ravines and fissures.
In most mountains, however, the lines of stratification are neither vertical nor horizontal, but intermediate between them, more or less sloping, as in most marked ranges of central Germany, for example. In such cases, the process of excavating river beds has been determined by various circumstances and conditions, and the direction of their channels does not alone depend upon the extent and tilt of the strata, but also on other forces which have exercised a favoring or a retarding influence on their direct course. The stratification has its influence, indeed, but it is general rather than specific. Still, it is very largely felt when it happens to coincide in its main lines with the direction of the mountain range, but is comparatively insignificant when it does not. We have instances in the Alps where the axis of stratification coincides with that of the main chain, from south-southwest to north-northeast; in the Jura, from southwest to northeast; and in the Scandinavian range, from south to north.
The different geological formations found in mountain districts have a very important influence in determining the direction of rivers. Mountains do not generally consist of rocks of one kind of structure, but of several. What stratification is to mountains whose geological formation is the same throughout, the superposition ofdifferent kinds of rocks is to those of composite materials. The layers may be divided into superior, inferior, and adjacent. These usually vary in respect to age, and may be traced in a regular geological seniority, as for example sandstone, gypsum, limestone, gray-wacke, and granite. These formations are either closely contiguous, or are separated merely by valleys, as for instance in the Carpathian chain, where the central granite knot is separated by valley plains from the more southern limestone chain; an example of contiguity is found on the west spur of the same Carpathian range. Wherever mountain systems of varied geological structure approach each other very closely, rivers seldom break their way through either one, but find their way along the roots of the mountains, till at last they come to a less confined place. Such river courses are often very large and deep; for the mountain streams which meet and are hemmed in by the narrow pass between the two contiguous ranges sweep all loose obstructions before them, and not only leave their path clear, but continually deepen it. We find this in the Ural, the Isère, the Rhone, Aar, Inn, in all the long and winding Alpine valleys, and in the Ebro, fed by the parallel ridges of the Pyrenees. The circle of rivers which girds the central Carpathian knot is an illustration of what was said a moment since. The Poprad, Dunayic, Arva, and Waag are found where the true Carpathian chain, which is granitic, is closely contiguous to subordinate ranges of limestone and gray-wacke. In any accurate map, the long, winding course between these two chains may be easily traced. Looking at the point where the Hartz Mountains and the Thuringian ridge touch at their roots, the groups are seen to be insulated, as it were, by the rivers which gird their bases. In the great streams of southern and southwesternAsia, too, the line of the water-courses can be traced along the narrow valleys which separate main from subordinate mountain chains; the Terek, Kooban, Koor, Aras, Euphrates, Tigris, Indus, Ganges, and probably the Chinese rivers, are all examples of this.
Some streams seem to be entirely independent of all these laws in forming their channels, and to have their direction assigned to them by the freaks of nature, such, for instance, as fissures in mountain chains and clefts, which remain to indicate ancient convulsions.
The entire course of a river is divided into three distinct and subordinate courses—the upper, middle, and lower. To these and their respective tributaries correspond the three grades of transition found on the banks, and which have already been alluded to. Not only the total amount of fall in the river bed, but also the angle of inclination, and the whole complex of phenomena in the basin, are reciprocal to the threefold character of transition in almost every hydrographical system in the world. Still, the variety of relations which arise from the combination of different elements is so variable, that an almost infinite diversity arises in the characteristics of rivers, and these characteristics always vary, too, according as found in the upper, middle, or lower course.
This begins at the ridge of the water-shed, and extends to the limits where the river emerges from the most rocky highlands. It depends for its existence upon the greater fall in the river bed there than lower down. At the upper course, therefore, rivers which may flow in exactly opposite directions are brought into direct neighborhood. The farther they advance from the water-shed the more they recedefrom each other. In the High Forest south of the Carpathian chain, and in the Bory Morass north of it, the waters which flow into the Baltic and into the Black Seas spring from the ground side by side. The name given to the districts where the head-waters of large and navigable rivers part is usually the French word portages, the English word transports being little used in that connection, although all, the German Trageplatze and the Russian Wolok, involve the idea ofcarrying, of porterage, from the head-waters of one stream to those of another. The lowest parts of a water-shed, the passes of a high mountain range, for example, the intermediate vales of lower ones, and the most elevated plains in flat districts, are the most suitable for the purpose of canal building, to serve as a connecting link between the sources of divergent streams; as, for instance, the canal which is proposed to connect the Baltic and the Black Seas by uniting the Vistula and Danube, the tributaries, the Poprad, Hernad, and Theiss being the channel of communication up to the mountains where a canal is to pass over the water-shed formed by the valleys of the Carpathian chain. Such a communication is the most available which can be made between the opposite sides of a mountain range. The practicability of constructing such canals depends very largely upon the degree of fall in the upper course of the connected rivers, as determined by the slope of the bed toward the horizon. The grade of most mountains’ sides, which stand back to back, is unlike on the two sides: steep on the one, slight on the other. Upon this depends the greater or less wildness of the streams flowing through their upper course. In the Ural chain the slope is steep on the eastern side, gradual on the western; in the Caucasus, steep on the north, gradual on the south; in the Carpathianand the Alps, just the reverse—steep on the south, gradual on the north. The rate of fall varies; but, in general, it lies between an angle of 2° and an angle of 6°, taking the entire upper course into account. On the very steep north side of the Pyrenees, the fall is between 3° and 4°; on the south side of the Alps, from the summits of Mont Rosa and Mont Blanc to the plains of Piedmont, it is 3¾°. It is far less in more unimportant ranges. And this angle, it should be remarked, is an average; it is the resultant of a great number of special, short slopes, which vary from the perpendicularity of an occasional waterfall to the equally occasional tranquillity of a meadow-like flow. The incidental slopes are, of course, much greater than the average of all. A grade of 15° is very steep; it is the maximum that can be ascended by a beast of burden. A grade of 8° is the maximum for wheeled vehicles; all roads must be less sloping than this. To accomplish the ascent of 35°, a man on foot must have some assistance. A grade of 44° in the high peaks of Mexico and Peru, Humboldt found inaccessible; only where the growth of trees and shrubs gave him an opportunity of planting his feet, could he climb where it was a little steeper than 44°. The Carpathians and the Pyrenees, on account of their steepness and their scanty verdure, are very difficult to ascend. The Alps are much more easily climbed than the mountains just mentioned, in consequence of their abundant growth of turf and undergrowth. The richest Alpine meadows of Switzerland have an inclination not exceeding 20°; at a greater slope the vegetation becomes more sparse. The grade on which it is possible for earth to cling, Lehman fixes at 45°, and considers that the normal slope, because at a greater angle, rain glances or ricochets. But Lehman is not right inassigning this as the normal slope possible for earth to cling and vegetation to grow, for on the Alps soil adheres and plants get a footing at a much steeper angle than 45°; in fact, the modifications in the appearance of the Alps, by the growth of trees clinging to steeper slopes than this, are very marked. From the highest possible grade where vegetation can get a footing, we advance to the sheer perpendicular.
The upper course of rivers is characterized rather by plunges than by equable flowing, and determines its way by a series of leaps through zigzag cuts and various ravines. It traverses bowl-shaped hollows and narrow defiles, and makes its way even through mountain lakes, depositing in them its residuum of sand and gravel which it has caught up and swept along. In its wild plunges it draws into its body considerable air, which appears as bubbles, and makes it a white mass of foam. By-and-by it reaches more level ground, becomes clear as crystal, and assumes a rich emerald green, or a deep blue. It is unnavigable, wild, romantic, and is always found in mountain districts.
The brawling brooks of Salzburg, of the Pyrenees, and of Sweden and Norway, all partake of this character. Those of the Pyrenees have a fall of an inch in every foot, and in some places cataracts of two or three feet. The same is observable in the Alps, where the continual stir of the water mixes in air enough to turn all into a mass of silvery-white foam. The Carpathian waters are the same before they reach the high plateaus lying at their feet. The Alpine lakes, too, which lie within the upper course of the rivers which feed them, have a considerable fall; Lago Maggiore, for instance, has a descent of 52 feet between Magadino and Arona.
In all the most marked mountain systems of Europe, the upper course of the rivers is especially prominent. Northern Europe is characterized by the fact that its streams have, throughout the most of their length, the peculiarities of the upper course—whether observed in northern Russia, in all Sweden, Norway, and Scotland.
With the exit of the river from the mountain district, all these relations are changed, and a new character begins.
Far more moderate is the descent after the river emerges from the mountain region, or where it has never experienced the wild turbulence of the upper course, as is the case in most of the rivers of eastern Europe. In the middle course the angle of inclination is much modified. The upper Main has a fall of 342 feet within three miles after leaving Fichtel Mountains. The descent of most of the rivers of central Germany is much less than this. The Neckar, whose sources lie 2084 feet above the sea, in passing to Heilbronn, which is 450 feet above the sea, falls at the rate of about an inch to every 32 feet. The fall of the Saale, after leaving the Fichtel range, is about 20 feet to the mile; that of Naab, about 14; that of the Eger, less; and that of the upper Oder, in Silesia, still less. More gradual yet is the slope of the Volga bed, which falls but 1400 in about 2050 miles, considerably less than a foot to a mile; and in its lower course its inclination must be still less.
The effects of the current must necessarily be very different from those observable under the influence of the dashing and wayward upper course.
The name River Bed is given to the entire breadth of the hollow which holds the river, and which varies inwidth according to the stage of the water, especially in large streams like the great rivers of America. The Mississippi is a mile wide at Natchez at low water, at high water almost thirty. The Orinoco, at St. Thomas, is three miles wide at low water, at high water it is over seventy. In the Volga and the Danube the stage of water makes great differences in the width of the river bed. In summer the depth and breadth are, as a rule, less than in winter.
The Channel differs from the river bed; it is the part of the river bed which gives life and motion to the whole current. In the upper course the channel and the river bed generally coincide; in the middle and lower courses, on the contrary, the channel occupies but a very small share of the whole bed, but yet it determines the direction, amount of fall, and the rapidity of the stream. It lies usually not in the middle of the river bed, but on one side; it passes, however, from bank to bank; it is indicated by the movement of ships, which always follow it, and it lies uniformly adjacent to the boldest shore. It widens the whole river bed toward one side, and not toward both; and so streams which traverse great plains, like the great Hungarian one, for instance, do not now run through the middle, but course along at the base of the marginal bluffs. In all such cases, it will be found that the channel hugs the boldest side of the bed. All the four Carpathian rivers, as they wind out between the main range and the subordinate ranges, have their steepest shore, not on the side of the loftiest, but on the side of the boldest mountains, and these are the ones of the subordinate range. So, in the plains which lie between the Swiss Alps and the Jura, the bold sides of the river bed lie on the side of the bolder though less important chain, and not on the side of the Alpine meadows. Thebold banks of the Ebro are not on the side of the Pyrenees and their plains, but on the south side. All the streams of South and Middle Russia have, therefore, on the east side, their low banks, on the west the bold ones; and this, because the most extensive plains lie on the eastern side.
In the more level tracts the windings of rivers are very much increased in magnitude. These windings check the current. The serpentine course is characteristic of rivers in their middle course, and it is repeated, though on a small scale, in every meadow brook. The serpentine course of rivers gives rise to countless islands and intervals: as, for example, between Bâle and the Rhinegau, but, with very few exceptions, no lakes, the characteristic feature of the upper course of rivers. But the broad meadow lands of the middle course very often indicate in the clearest manner that they were once lakes of considerable magnitude, which have subsided and left their basin a dry plain. An example may be found in the meadow land of the Rhine, from Bâle to Bastberg, below Strasbourg, and again from Ladenburg, in the Palatinate, to Bingen. So on the Danube, from Ulm to Passau, Lintz, and Kloster Newburg, and again from Pesth to Beloro Semlin, as far, in fact, as the narrows at Orsova. The same feature is met in the middle course of the Volga, from Tver eastward to the west Ural, and southward to Saratov and Kamishin, where it breaks through the Obstshei-Syrtis, which was, doubtless, once the barrier of a great inland lake. In these basins, now dry, there is a surprising uniformity of characteristics wherever on the globe they occur. They differ but little, whether found in the middle course of the Ganges, the Indus, the Euphrates, or the American rivers. The still, incomplete stream ofthe St. Lawrence shows us, even in the present, what the ancient conditions were before they solved the problem of their complete development. There, a row of such lakes as formerly existed in the now fruitful plains of the middle Rhine, the middle Danube, and central Russia, are the five great Canadian lakes. They still constitute the middle course of the river, and one pours itself directly into another, either over a gentle slope of land, or in a great cataract and rapids, such as we do not observe in the middle course of other streams, which are not, like the St. Lawrence, incomplete. Only when waterfalls disappear can the inclination of rivers become a gradual one. The uniformity of the grade of their channel is, therefore, a sign that they have attained to a complete development. In such, slight rapids remain, instead of the ancient cataracts. The existence of those primeval falls we find in all rivers, even in the Rhine and Danube. The rounded faces of the rocks which once were the barriers to the rivers’ course, and the debris once swept down from the mountains and deposited over the bottom of the ancient lakes, show this.
The strongest instance of cataracts, resembling the ancient ones which connected the lakes of nearly all the great rivers of the globe, is seen in the fall of Niagara. That cataract is an epitome of the falls of all other streams. The Niagara River conducts the water of Lake Erie, by a channel 33 miles long, to Lake Ontario, 300 feet below it. At the Great Fall the river plunges about 150 feet into a chasm which it has hollowed out from the soft stone between the two lakes. The cataract was formerly seven miles below its present location, and has been observed to be steadily working backward since its discovery. In the distant future it will, doubtless, wholly disappear, asall others have done. For the Niagara is merely a striking instance of a principle once universal, but which merely worked itself out on a smaller scale. The more fragments of rock and mountain debris were swept along, the sooner were the primitive falls rent away by the wash and the percussion, and the development of the middle course completed.
The places of transition which lie between the higher dry basins and the lower ones are still to be traced in almost all rivers; not by great waterfalls, which belong only to the upper course, but by simple rapids. They are more or less characterized by narrows, with steep, rocky banks, where, doubtless, cataracts existed in the primitive times. They are recognizable by this feature, that they are uniformly alike, and distribute their force equally on both sides of the river. Examples may be found on both sides of the Rhine, in the narrows between Bingen and Bacharach; on the Elbe, from Tetshen to Shandau, Dresden, and Meissen. In these places the rivers have a very tortuous course, and there are whirls and rapids (rapides, sauts, of the French; saltos, randales, of the Spanish; schewerin of the Russians) which impede navigation. In these localities the entire aspect of nature is changed, and the landscape becomes exceedingly beautiful. Here we find ancient narrow roadways; here are places of great historic interest, and of great interest to the naturalist, assuredly not of accidental origin, but in close connection with the development of the river bed, and in close analogy with all places of transition from highland to lowland.
We may, perhaps, mark these features in all the rivers of the earth. A knowledge of them is essential to understand thoroughly the natural development of a river systemin its true parts; unfortunately, they have as yet been too little observed and described. Among European rivers they are found in the Guadiana, at the Saltos de Lobo; in the Douro, at the rapids below Torre de Moncorvo; in the Ebro, at Sastago, below Saragossa; in the Rhone, the rapids below Lyons, between the granite banks of Pierre Encise; in Loire, by Iguerando, below Roanne; in the Rhine, below Strasbourg, and at the narrows at Bingen, near St. Goar and Andernach; in the Weser, at the Porta Westphalica; in the Danube, at Grein, at Kloster Newburg, and at Yachtali, Drenir Kapi, (Iron Gate,) and Orsova; and in the Dnieper, the thirteen waterfalls below Yekaterinslav. The same features are repeated in all the other streams of Europe and the remaining continents. More close investigation of them will lead to important results, concerning the structure of the earth in the regions intermediate between plateaus and lowlands.
As a high grade, great cataracts, sharp and bold cliffs, and mountain lakes characterize the upper course of streams, so rapids, dry lake basins, and a meandering channel characterize their middle course. Below the lowest rapids are found the level plains or lowlands which give rivers their third characteristic.
As soon as the rivers break through the lowest range of hills which once beset their course, they deposit the debris which they bear with them, and begin the formation of diluvial plains. We find in the soil of all level places along the middle, as well as the lower course of rivers, traces of the same kinds of rock and minerals, which characterize the mountains where they rise. The rate of fall in the lower course of rivers is so slight as tobe almost imperceptible. Relatively, it is the greatest in the Volga; from Kamishin to the Caspian the descent is more than 150 feet, although the distance is less than 500 miles. The Senegal, from Podor to the sea, a distance of about 200 miles, falls only about 2½ feet; the Amazon, within about the same distance, falls only 10½ feet, or about an inch to the mile. In such rivers, therefore, the tide can flow a very long way inland.
This gives rise to a great conflict of forces—the pressure of the stream in its natural flow, heightened at the appropriate season by the annual inundation, and the backward pressure of the tidal wave. Before these forces come into equilibrium, the river bed is constantly changing. The river proper seeks this equilibrium by a parting of its channel, dividing into two mouths, as in the Nile, or into more than one, as in the Rhine and Danube, or several (about 65) in the Volga. The momentum of the stream, the resistance of the tide, and the consequent slow speed of the current promote the fall of deposits along the lower course of rivers. Below the surface the result of these deposits is found in sand banks or bars; above the surface, as low, marshy land, the deltas, subject to frequent inundation. We see this in the Rhine, the Nile, the Euphrates, the Indus, the Ganges, the Mississippi—in all, about fourteen of the first-class rivers of the globe. The contrary feature, single, broad mouths not yet filled up by alluvial deposits, negative deltas, or deep ocean inlets, can be observed in nine others of the largest rivers—the Obi, Yenisei, St. Lawrence, Columbia, La Plata—mostly found, however, in the north of the earth, where there is very little of the more loose and fruitful soil which more southern rivers bear onward from the mountains where they rise.
Another peculiarity of the lower course is seen in the extraordinary changes in the river bed—the shifting of the channel from one side to the other. This is the natural result of the very light and movable character of the deposits brought down from above, and the strong pressure of the current, which, though slow, has great momentum. In the lower course of the Ganges, Indus, Euphrates, Nile, Rhine, and Po, these changes can be traced as a matter of history, and, in the lapse of centuries, have had great influence on the formation of the great plains of those rivers’ mouths and on the people living there. With the lower course begins the regular yearly inundations, which cover vast districts in tropical countries; and to these inundations may be attributed the gradual raising of the level of the plains covered by them. Hence arose Herodotus’ descriptive phrase ποταμοὶ ἐργατιχοί, (prolific rivers.) The great fruitfulness of these lowlands is well known. The rich alluvial deposits have made Bengal, Babylonia, Egypt, Lombardy, Holland, and the Netherlands the granaries of all neighboring countries.
In proportion as the mouth of great rivers resembles an inland sea, having a strongly marked tidal flow in sympathy with the ocean, does the whole nature of the lower course vary. The rivers whose mouths are turned to the east and south are those which are exposed to the strongest and the highest ocean waves. Such are Chinese, Indian, and South American rivers, which sometimes show the result of this, 500 miles inland. The tide extending so far into the interior facilitates navigation very much, and transforms the lowlands along their margin into districts, which seem transitional between true continent and oceanic islands. All the mouths of first-class rivers which open toward the north and west are less deeply affectedby the entrance of the sea waves. To these belong most of the European streams. Exceptional to both of these classes are the three rivers, the Nile, Danube, and Volga, whose direction is not toward the ocean, but toward the center of the Old World. They form a triad, not of oceanic, but of continental streams; in them there is no ebb and flood. Their lower course and mouths must, therefore, display different relations from those of any other of the great rivers of the globe.
It was early remarked that not all streams, when they reach the sea, flow at once into it, but come to a standstill. It is so with the Thames, and with most of the North American rivers. The ocean sometimes throws a tidal wave twenty to thirty feet high up their channel, and dams their flow. Rivers vary exceedingly in their relations to this high barrier. The Chinese streams are sometimes raised forty feet by it above their normal level. This gives rise to a salt oceanic river, so to speak. It is the same with the Thames at London. At high tide the surface is salt, while the water at the bottom is fresh. The struggle with the downward current and the upward current is very often visible. It is so in the Orinoco, the Ganges, in the Chinese rivers; most of all, in the St. Lawrence.
In all the continents there are many small rivers and rivulets which have no normal mouths; which lose themselves in the earth before they reach the sea. Sometimes they pursue a subterranean course, and emerge again, though usually with a changed name. Among the best-known of such instances is the Perte du Rhone, below Geneva, where the river flows for a little way directly beneath a spur of the Jura Mountains. In like manner, the Meuse, which loses itself in the earth at Bazoilles, in the VosgesMountains, west of Nancy, flows in a subterranean bed as far as Noncourt, nine miles distant, and then emerges. The phenomenon is common among the Jura, and in the limestone cliffs which feed the Drave and Save. The tourist meets almost hourly there some brook or little river disappearing beneath the ground. On the high Asiatic plateau of Gobi, 68 rivers are known, which disappear in a similar manner; in the north of Thibet there are 115 such. They are common, also, in the Chinese province of Yun-nan, on the Persian highland, and on the plateau of the Bechuanas, in South Africa. In South America, between the Andes and the La Plata, there are twelve lakes without effluents, the greatest being Lake Titicaca. In Central America, there is the Lake of Mexico.
The division of the whole length of a river into the three courses—the upper, middle, and lower—and the proportionate share which each of these bears to the whole, depends upon the height at which the source stands above the mouth. The greater or less extent of the transition grades, and the greater or less extent of navigable waters, also depend on the same. The upper course has, as a general rule, too many hinderances to be very valuable for navigation; it is, at best, adapted only to boats. The more united and deeper middle course offers facilities for vessels of considerable draught; yet the frequent sunken rocks and eddies and rapids are a great impediment to navigation. We find it so in the Rhine, below the Falls of Schaffhausen, as far as Bâle; and in its middle course, at Bingen and St. Goar; in the Danube, also, at Grein and Orsova.
The lower course, on the other hand, opens like a broad fresh-water sea, that sometimes allows large ships to sail 50, 200, and even 500 miles inland. These maritimestreams ought to be discriminated from others; the Chinese call them “sons of the ocean.”
The proportions in the length of the upper, middle, and lower course of rivers are exceedingly variable; and equally variable of course are the transition lands apportioned to each, and forming its natural supplement. The upper course of the Volga is very short, the middle very long, and the lower very short. The same relative proportions, though with very different dimensions, are found in the Vistula, the Ganges, the Euphrates, and the Mississippi. The upper course of the Rhine, on the contrary, is very long, through all Switzerland to Bâle; the middle also very long, to Cologne; the lower, very short, to Rotterdam and the sea. It is the same with the Nile, the Danube, and the Indus. In the Marañon or Amazon the upper course is very short, the middle and lower very long. In the Chinese rivers Hoang-ho and Yang-tse-Kiang all the three courses are relatively long.
The length of the middle and lower courses, although important conditions of navigation, are not the only ones. Others are not to be overlooked,—the amount of water, depth of channel, and the like. These, however, are not capable of being generalized under any law, but depend upon the individual characteristics of each stream. Every river needs, for an exhaustive account of its features, its own monograph.
There remains but one important point to be considered—one which has exerted a very great influence on the diversity of structure in all river systems, controlling the area of their drainage, their volume of water, their effect on human culture, and on the ethnographic character of the people dwelling on their banks. It is the distance from the source to the mouth in direct distance comparedwith that following the tortuous course of the stream. The two lines almost never coincide; they generally lie far apart. And the less they approach to coincidence, the greater becomes the area of the river basin; the more numerous and valuable the tributaries to the main course, the greater the volume of the stream and the more varied and extensive its influence.
One or two examples drawn from European rivers will more fully explain this point, to which Buache has already called attention in his “Parallèle des fleuves.”
The mouth of the Volga is 982 miles distant from the source, in an air-line. The distance, including all the curves of the stream, is 2012 miles, the bendings adding 1028 miles to the direct course. By this doubling of the shortest possible distance, the area drained by it is swollen to the enormous size of 657,000 square miles. The direct course lies in a diagonal direction from northwest to southeast; but the real direction is a changing one. First, it flows a short distance from north to south, then in its middle course it has a double direction; first eastward, toward the Ural chain, then to the south, and lastly, in its lower course, to the southeast. Through this varied course it receives tributaries from very remote sources, and waters a country altogether greater than would be possible if the Volga’s course were direct from the source to the mouth. Its basin becomes so large as to embrace a fifth of Europe, and the stream becomes one of the longest and most available for navigation in the continent. The vastness of the volume of water and the wandering course have both contributed to the value of the Volga lowlands.
The exact contrast to the Volga is found in the Dniester. In the Volga there is a maximum of windings; in the Dniester there is a minimum. The air-line distance ofthe mouth of the Dniester from the source is 408 miles; the distance, including all the bends, is 450 miles; the loss in winding is, therefore, but about 42 miles. The theoretical course of the Dniester,i.e.measured by an air-line, would coincide very nearly with its actual course. There cannot be, therefore, any distant springs whose waters flow into its channel; its basin is one of the most contracted in the world in consequence of its directness; and a small belt, embracing but 32,850 square miles, comprehends the entire district that it drains, freed from all those tributaries which make the Volga basin so important.
The Dnieper, its eastern neighbor, is 630 miles in direct distance from the source to the mouth, but 1000 with all its windings; leaving 370 miles as the extraneous shore, which adds to the value of the basin, and contributes to the 219,000 square miles which it drains.
The same contrast is seen elsewhere, though not on so extended a scale. It is to be found in the Vistula, Oder, Elbe, Weser, Rhine, and Danube. These rivers give shape to the transition terraces between broad eastern Europe and the more contracted western portions of the continent; their dimensions are, therefore, on a less extensive scale than in the great Russian streams. Still, the differences in them are worthy of notice.
In the Vistula, the direct distance from the source to the mouth is 329 miles, and the real distance is 611 miles; the windings comprise, therefore, 280 miles, or about two-thirds of the air-line from extreme to extreme. It becomes able to receive a large number of tributaries, and its basin is enlarged to an area of 78,402 square miles, becoming one of the best-watered and most fruitful on the globe.
In the Oder, the direct distance from the source to themouth is about the same as in the Vistula. But while the latter frequently changes its course, running first northward, then eastward to the Sau, then northward again to the Bug, then westward to the Drewenz, and lastly northward, and so gains a very large basin of drainage, the former is unvarying in its course from southeast to northwest; so that the direct line drawn from extreme to extreme, as the bird flies, is nearly coincident with the actual course of the river. The windings do not, at most, comprise one-third of the whole length of the stream, and the basin drained by its tributaries is at least a third less than that of the Vistula, and is proportionately less valuable to the interests of the world.
In the Elbe the air-line length is 394 miles, greater therefore, than that of the Vistula or the Oder; its length, including its windings, is about the same as that of the Vistula. The area of its basin lies therefore between the two, 61,320 square miles; it is more valuable, therefore, than that of the Oder, and less valuable than that of the Vistula.
Still less striking in this respect are the Weser and the Ems; but the Rhine assumes a prominence, in relation to the value of its basin, greater than even the Vistula. The direct distance from the source of the Rhine to its mouth is 423 miles, the actual distance 705 miles; the windings comprise, therefore, more than two-thirds of the entire length of the stream. The number of tributaries is uncommonly large, the area drained is increased about 9855 miles beyond that of the Vistula; and the entire basin (88,257 square miles) is one which has been of the greatest import in the history of all central Europe.
All the rivers and all the terrace lands of the globe exhibit the same relation which we have been briefly indicatingin a few European ones; in some of the great rivers of the world they are to be traced on a scale of grandeur of which in those which have been touched upon scarcely a suggestion is given.
But not in this feature, added to what has been already said, do we exhaust the fruitful subject of Rivers, and the terrace systems which accompany them from their source to the sea. The diversity of phenomena traceable in them had hid their unity from geographers, and prevented their tracing general principles in so manifold details. The dry, linear representations on most of our maps have blinded the eye to the living and organic relations which river systems enter into, and through which they exert a great influence. They must be examined singly; they must be studied in their real character and individuality, and each must have its own monograph, before we can fully know the value of river systems to the world.
We have now to touch upon one or two points omitted, thus far, in our discussion of the hydrography of the continents.
The stream is a unit; most streams have a single channel as the last goal of their descent. Others may have double channels, which contend with each other for the superiority. If they are double only for a part of the whole length of the river, and in the upper or middle course flow together, and form one main channel, they can be called twin head-streams. We have an example in the Danube and Inn, which are equally long and equally large. Other instances are the Rhone and the Saone, the Volga and Kama, the Missouri and Mississippi, the Blue and White Nile, the Ganga and Jumna. Others have triple head-streams; as, for example, the Hither, Middle, and Farther Rhine; the Ucayale, Huallaga, and Marañon, whichcombine in the middle course to form the Amazon. There may be even five head-streams, as in the Indus. Often it is only through the usage of speech, often through ancient and exploded errors, that the name of one of the head-streams is given to the whole river.
If the double channels continue through the whole length of the river system, they belong to a different category; they become true double systems, and have a double influence on the development of the whole range of terraces from source to base. From their meeting in a common bay or gulf at the mouth, they may be called sister-streams; and, from the territory which they inclose between them, the Mesopotamia, they may be called Mesopotamic streams. Between such double streams some of the greatest States of Asia lie. Universally known, on account of their influence on Asiatic culture, are the Euphrates and Tigris uniting in the Persian Gulf, Ganges and Brahmapootra uniting in the Bay of Bengal, Gihon and Sihon in the Sea of Aral, Hoang-ho and Yang-tse-Kiang encompassing the Central Flowery Country of the Chinese Empire, and meeting in a common delta. These double streams are mostly met in Asia, and they have exercised a great influence on the whole growth of oriental civilization.
In South America there is yet another and more complex form yet of river system. The Amazon is connected with the Orinoco by means of the little cross-river Cassiquiare. By this connection the middle course of both rivers is made more available to navigation than it would otherwise have been. Such cross-streams may be found, though on a smaller scale, in other continents; in Africa, for example, between the Senegal and the Rio Grande. There a network is made between the parallel rivers, butit is available for navigation only in the wet seasons. In Central Africa there seems to be a similar phenomenon between the eastern tributaries of Lake Tchad and the western tributaries of the Bahr el Abiad or White Nile, though this rests on the authority of the Arabs. In India there appears to be a similar connection between the middle course of the Indus and the Jumna, and so the Ganges, by the mediation of the Sarasvati or Histara and the Gharghara. There may have been the same in Central China, between the Hoang-ho and the Kiang, where the Imperial Canal now runs; and a similar feature may be found in the Lithuanian marshes, connecting the Vistula and Dnieper river systems, through the mediation of the Bug and the Przypec. The skill of man has, in many places, accomplished the same end by the construction of canals.
Although all rivers, in the course of their development, follow the universal law which leads them from their source, however high, to the sea, yet there is, even in their descent, scope for exceedingly varied phenomena. It is not necessary that everywhere a strongly-marked line of water-shed should exist, but often, as in all the more level plateaus, there are broad, neutral plains which perform the function of water-sheds, though possessing no decisive character. It is so through a great part of Central Asia, in the low plains of Australia, probably in a large part of Africa, and so markedly in America, that all lines of water-shed wholly disappear, and the rivers flow confusedly together, without any system, and in obedience to no law.
Some rivers come down the sides of high mountains in torrents, then course around in a long, winding course, turning out for all obstacles, and at last find the sea.Others are entirely unlike them. The Ganges flows from the south side of the Himalaya Mountains, and courses along their base, following the direction of the chain in a southeasterly direction, till it reaches the Bay of Bengal. The Indus springs from the north side of the Himalaya, flows northwest over the plateau of Little Thibet as far as Iskardo, then breaks through the whole chain to pour itself out upon the lowlands of India, the Punjaub, and Mooltan. Dashing its way through the most formidable barriers, it is entirely unlike the gentle Ganges, which pursues its tranquil course through the plains, meeting no barrier in its entire length. The Indus, so long as it remains north of the Himalaya, traverses a plateau 10,000 feet above the sea; while the Ganges, even at Delhi, is but 1000 feet above the sea. Both rivers, although represented in precisely the same way upon the maps, have an entirely different physical character.
The same difference in structure occurs in the streams of other continents, and even in those of Central Europe, though on a less colossal scale. There are, therefore, classes of rivers, and they ought to be just as sharply discriminated as the classes in botany and zoology.
Plateau streams, such as the Danube, as far as the Lower Austrian and Hungarian plains, and the Saone, down to its confluence with the Rhone, pass through high, uniform plains with little fall. They are genuine mountain followers, springing from the verge of the chain and crossing along its base, the Saone taking the west side of the Alps, as the Danube does the northern, and the Po the southern.
The rivers which force their way through mountain ranges form a second class. The Rhine, a free child of the Alps, from its source to the sea, breaks through allthe ranges up to the Jura; then it forces a path through all the mountains of Central Germany, till it comes to its lower course. It may, therefore, be classified with the Indus. It leaves the Alps suddenly at Bâle, and opens a new and romantic way through no insignificant obstacle, and is everywhere a conqueror. That is the peculiarity of the Rhine.
Two streams of analogous nature, though less marked in their characteristics, are the Elbe and the Weser. But these both rise, not among the Alps, but amid the German mountains. They lack, therefore, the exceedingly romantic character of Alpine rivers; but they do not lack in picturesque scenery, and this they owe to the obstacles which they pass. The Elbe has broken its way from the Bohemian ridge through the so-called Saxon-Switzerland, as far as Meissen, and the Weser from the fissures of the Werra and the Fulda to the Porta Westphalica. The Elbe and the Weser make, with the Rhine, the triad of Central European rivers, which have broken a pathway for themselves through mountains which impeded their course.
A third class of rivers are those which encounter no obstacles, and flow in a placid stream from the source to the mouth. They extend in Europe from the Vistula to the Ems, including the Oder and excluding the Weser and Elbe, and from the Rhine along the whole Atlantic coast of France, embracing the Seine, Loire, Garonne, and the Adour—all of these having, in greater or less degree, the same hydrographical character.
From these can be still further discriminated the subordinate coast rivers.
To a fourth class belong all those tributary streams, of whatever size or length, which agree in possessing noindependent character, and do not pour their waters into the sea through their own mouths.
The application of this system of classification can be applied to the streams and their accompanying terrace lands in the other continents. But these observations may suffice to indicate the general principles which we would apply to the study of rivers, and leave to the student their further application.
The great typical forms already considered, highland, plateau, mountain, lowland, terrace, and river, which all claim so large a share of attention in studying their physical characteristics, are no less worthy of careful attention, in consequence of their influence on human culture. Our account would not be complete without devoting a few pages to the consideration of the manner in which nature and history have reacted on each other.
The most elevated highlands, the loftiest plateaus, uniform in their aspect, immense in their extent, isolated, without trees, having the thin soil characteristic of steppes, and useful only for grazing, are the home of the primitive nomadic races. Without forests and without shelter, without valleys and without water-courses, with sandy and rocky soil, covered with a scanty vegetation, they serve only to supply food for the gregarious animals which follow man, and to furnish a home to wandering tribes of herdsmen. Instances are found in Central Asia, in Toorkistan and Persia, in Central Africa, including the Galla tribes and the Abyssinians. So, too, among the high plateaus of America, the home of the primitive Aztecs. From such places came the first movements of emigration; from the high plateaus of Central Asia came the wanderingPersians, Huns, Mongolians, and Turks; and the same course of emigration was witnessed among the negro tribes of Central Africa, proceeding from the Galla tribes. The lower highlands, less colossal in size, of more moderate height, and of more genial temperature, have at all times reached a certain low stage of culture, after giving a home to the nomads from the higher plateau; but have never developed that culture to any considerable extent. We find examples of this in the high terraces of Bootan, the Deccan, and Persia; in Africa, among the Atlas mountains; in Abyssinia, in the ancient Greek Arcadia, in Castile, in Arvernia, (Auvergne,) in Gallia, in Hesse, in the Eifel, and on the Valdai hills.
In the exceedingly complex, subdivided, and romantic mountain districts of the globe, the races have attained, by virtue of the variety of their resources and the energy of their stock, to the highest results of civilization, and have manifested the most independent and progressive spirit. In such regions, hunting, working in wood, the settled life of shepherds, working in metals, agriculture on such terrace lands as those of Nepaul, Cashmere, Palestine, the Lebanon, Apennine, and other ranges, fruit culture, tilling vineyards, the cultivation of all kinds of industry, as in Central Germany and in most regions of the temperate zone, develop most thoroughly and speedily the culture of a people. In such occupations men learn to lean more on each other, and grow into that diversity of occupation and division of labor, which are the latest results of civilization. The Zend, the Sanscrit, and the Persian nations which people the fertile tracts at the base of the Himalaya Mountains, from Maghada, Lahore, Nepaul, and Cashmere, as far as Persepolis and Hamadan, Susa and Shiraz, the inhabitants of the hill country of Palestine andSyria, those of the Tehama range of mountains in Arabia, those in the moderately elevated meadows of Gondar, as well as those in all the European Alpine lands, Switzerland, Tyrol, Styria, as well as the inhabitants of the mountain region of Peru and Mexico, all attain to an early and considerably advanced state of civilization. Other nations have found in mountains asylums in time of danger—the Tsherkeses and Ossetes among the Caucasus, for instance, the Basques among the Pyrenees, and the Gorals among the Carpathians.
The lowlands, as soon as the water had left them enough to make them habitable, have become, from the first, the abodes of a teeming population; and there has been the same blending of races in the most ancient as in the most recently settled, in China as in Texas, and, in truth, all North America. Often these inroads of population have been a source of injury, as has been the case in the northern Siberian plains, where the Finnish tribes have made their homes, and in the waste of Sahara, where the Barbary tribes, the Bedouins, the Tibboos, and the Tuaricks have made their retreat.
On the fruitful terraces, along the middle course of rivers, the earliest fixed habitations and ripened culture have been attained. Through the traditional handing down of past results, and by the habits of peace, their inhabitants have more thoroughly subjected nature and advanced to a higher state of civilization than the dwellers in the interior, away from the rivers. It has been the same, in a great measure, with the lower course, as, for instance, in Egypt, Mesopotamia, China, and Bengal; and in Europe, in Lombardy, Holland, and the Netherlands, where, to the efforts to recover land from the sea, have been added fishing and commerce. On such fruitful tracts asthe mouths and middle courses of rivers water, nations could find a permanent home, and pass quickly to all liberal and refining arts and occupations. This is clear, from the instances of the eminent monarchies of the East, Meroe, Thebes, Memphis, Babylon, Nineveh, Bagdad, and Mosul. So, too, on the Indus and Ganges, in the domains of Taxila, Maghada, Benares; and later in the great empire, whose centers were Agra and Delhi. China has arrived at its highest civilization in the fertile district between its two greatest rivers. Greece and Rome are marked exceptions. Their progress they owe, not to great river basins, but to their peninsular form in the middle of the coast of a delightful sea, full of islands and surrounded by lands in a greater or less advanced state of civilization. England’s peculiar maritime position has given it its wonderful vantage-ground for progress in all human culture.
In the east of Europe, the basins of rivers have exercised the same influence, to a certain extent, that has been hinted at above; and Moscow, Kiev, Cracow, and Warsaw remain the seats of a civilization which, rude as it was, owed its existence to the physical conditions of the great Sarmatian river systems. In western Europe, the less marked features of the country have contributed to the peculiar historical development of the continent. The rich deltas have become the granaries for a large part of the population, allowing industry to flow into other channels besides agriculture. The sea-faring habits of the people along the coast have broken up and done away with what is special and provincial, and have conferred a cosmopolitan manner of living upon the entire population. It was the same with the Phenicians in ancient times, with the Portuguese in the middle ages, as it has been with the English, Spanish, and Dutch in modern days. Fishing,navigation, and trade have become permanent necessities of civilization. In the heart of continental Europe, the rivers have had a great influence on the progress of nations; the North German streams have extended their effect from the abode of the ancient Saxons along the Baltic as far as the home of the Salic Franks on the Scheldt, Seine, and Loire; the Danube, with its complex and important system of terraces and lowlands, has opened communication between South Germany and Hungary, Wallachia, and the East. The Vistula, Oder, Elbe, and Weser have connected the homes of the old Sclavic population with the Scandinavian coasts and the land of the Angles and Saxons at the neck of Denmark, to the equal advantage of both. The great terrace system of the Rhine, embracing the Odenwald, Hardt, Spessart, Taunus, Hundsrück, Eifel, and the Siebengebirg, has thrown into the most active industrial and commercial relations the whole district which it waters. It opened a way to the Romans in their conquering advances before it did to the tribes of Helvetia, Gallia, Germania, or the Lowlands: it sundered those tribes, and kept them from preying upon each other; but, in the advance of civilization, it has become one of the strongest bands to knit together the central countries of Europe.
The Danube, with its extensive terrace lands, faces the east, and has, therefore, very different relations to European history from the Rhine. It is a double-headed river, and one of its head-streams, the one which bears the name of the river proper, extends almost to the Rhine basin; while the other, the Jura, has its source in Grisons, and hard by the head-waters of the Rhine. As the Danube connects the Caspian and Black Sea basin with western Europe, and the largest part of the Asiatic immigrationshave followed its course, the Danube has become the great avenue between Europe and Asia. Celts, Teutons, and Romans were mingled even before Christ, in Noricum, Vindelecia, Bavaria, and Suabia. How many tribes may have been crowded westward by these, is unknown to us. The same fate has happened to the people who settled there before Christ, and the inroads of the Huns, Goths, and other tribes of similar origin, scattered the older inhabitants over all Central Germany. We know, too, that Sclavic, Hungarian, and Turkish incursions followed, each one dispossessing wholly or in part the one which preceded it.
All great rivers and river systems have had a similar influence on the course of civilization. There is not a single type feature in the world which has not contributed its part to the advance of the human race; no one is without its place and its function.