Graham's Magazine, Vol. XLI, No. 5, November 1852. VariousЧитать онлайн книгу.
of secondary and alluvial districts flow with slow but powerful current, between low and gradually descending banks, which, being composed of soft rocks or alluvial grounds, are easily worn away by the waters, and hence great changes are effected in their channels, and a peculiar color is given to their streams by the earthy particles with which they are charged. Many rivers have their names from this last circumstance. The Rio Negro, or Black River, which flows into the Amazon, is so called on account of the dark color of its waters, which are of an amber hue wherever it is shallow, and dark brown wherever the depth is great. The names of the two great streams which unite to form the Nile, the Bahr-el-Abiad, or White River, from the Mountains of the Moon, and the Bahr-el-Azrek, or Blue River, from Abyssinia, refer to the color which they receive from the quantity of earth with which they are impregnated. The united rivers, for some distance after their junction, preserve their colors distinct. This is the case likewise with the Rhine and the Moselle; the St. Lawrence and the Ottawa. The Upper Mississippi is a transparent stream, but assumes the color of the Missouri upon joining that river, the mud of which is as copious as the water can hold in suspension, and of a white soapy hue. The Ohio brings into it a flood of a greenish color. The bright and dark red waters of the Arkansas and Red River afterward diminish the whiteness derived from the Missouri, and the volume of the Lower Mississippi bears along a tribute of vegetable soil, collected from the most distant quarters, and of the most various kind – the marl of the Rocky and the clay of the Black Mountains – the earth of the Alleghanies – and the red-loam washed from the hills at the sources of the Arkansas and the Red River. Mr. Lyell states that water flowing at the rate of three inches per second will tear up fine clay; six inches per second, fine sand; twelve inches per second, fine gravel; and three feet per second, stones of the size of an egg. He remarks, likewise, that the rapidity at the bottom of a stream is everywhere less than in any part above it, and is greatest at the surface; and that in the middle of the stream the particles at the top move swifter than those at the sides. The ease with which running water bears along large quantities of sand, gravel, and pebbles, ceases to surprise when we consider that the specific gravity of rocks in water is much less than in air.
It is chiefly in primary and transition countries that the rivers exhibit those sudden descents, which pass under the general denomination of falls, and form either cataracts or rapids. They occur in secondary regions, but more rarely, and the descent is of a more gentle description. The falls are generally found in the passage of streams from the primitive to the other formations. Thus the line which divides the primitive and alluvial formations on the coast of the United States, is marked by the falls or rapids of its rivers, while none occur in the alluvial below. Cataracts are formed by the descent of a river over a precipice which is perpendicular, or nearly so, and depend, for their sublimity, upon the height of the fall, and the magnitude of the stream. Rapids are produced by the occurrence of a steeply-inclined plane, over which the flood rushes with great impetuosity, yet without being projected over a precipice. The great rivers of England – the Thames, Trent and Severn – exhibit no example of either cataract or rapid, but pursue a generally even and noiseless course; though near their sources, while yet mere brooks and rivulets, most of our home streams present these features in a very miniature manner. A true rapid occurs in the course of the Shannon, just above Limerick, where the river, forty feet deep, and three hundred yards wide, pours its body of water through and above a congregation of huge rocks and stones, extending nearly half a mile, and becomes quite unnavigable. Inglis had never heard of this rapid before arriving in its neighborhood; but ranks it in grandeur and effect, above either the Welsh water-falls or the Geisbach in Switzerland. The river Adige, in the Tyrol, near Meran, rushes, with resistless force and deafening noise, down a descent nearly a mile in length, between quiet, green, pastoral banks, presenting one of the most magnificent spectacles to be met with in Europe. The celebrated cataracts of the Nile are, more properly speaking, rapids, as there is no considerable perpendicular fall of the river; but for a hundred miles at Wady Hafel, the second cataract reckoning upward, there is a succession of steep descents, and a multitude of rocky islands, among which the river dashes amid clouds of foam, and is tossed in perpetual eddies. It is along the course of the American rivers, however, that the most sublime and imposing rapids are found, rendered so by the great volumes of water contained in their channels. The more remarkable are those of the St. Lawrence, the chief of which, called the Coteau de Luc, the Cedars, the Split Rock, and the Cascades, occur in succession for about nine miles above Montreal and the junction of the Ottawa. At the rapid of St. Anne, on the latter river, the more devout of the Canadian voyageurs are accustomed to land, and implore the protection of the patron saint on their perilous expeditions, before a large cross at the village that bears her name. The words of a popular song have familiarized English ears with this habit of the hardy boatmen: —
“Faintly as tolls the evening chime,
Our voices keep tune and our oars keep time.
Soon as the woods on shore look dim,
We’ll sing at St. Ann’s our parting hymn.
Row, brothers, row, the stream runs fast,
The Rapids are near, and the daylight’s past.
“Utawa’s tide! this trembling moon
Shall see us float over thy surges soon.
Saint of this green isle hear our prayers,
Oh, grant us cool heavens and favoring airs.
Blow, breezes, blow, the stream runs fast,
The Rapids are near, and the daylight’s past.”
The Kaaterskill Falls here represented are celebrated in America for their picturesque beauty. The waters which supply these cascades flow from two small lakes in the Catskill Mountains, on the west bank of the Hudson. The upper cascade falls one hundred and seventy-five feet, and a few rods below the second pours its waters over a precipice eighty feet high, passing into a picturesque ravine, the banks of which rise abruptly on each side to the height of a thousand to fifteen hundred feet.
In the grandeur of their cataracts, also, the American rivers far surpass those of other countries, though several falls on the ancient continent have a greater perpendicular height, and are magnificent objects. In Sweden, the Gotha falls about 130 feet at Trolhetta, the greatest fall in Europe of the same body of water. The river is the only outlet of a lake, a hundred miles in length and fifty in breadth, which receives no fewer than twenty-four rivers; the water glides smoothly on, increasing in rapidity, but quite unruffled, until it reaches the verge of the precipice; it then darts over it in one broad sheet, which is broken by some jutting rocks, after a descent of about forty feet. Here begins a spectacle of great grandeur. The moving mass is tossed from rock to rock, now heaving itself up in yellow foam, now boiling and tossing in huge eddies, growing whiter and whiter in its descent, till completely fretted into one beautiful sea of snowy froth, the spray, rising in dense clouds, hides the abyss into which the torrent dashes; but when momentarily cleared away by the wind, a dreadful gulf is revealed, which the eye cannot fathom. Upon the arrival of a visitor at Trolhetta, a log of wood is sent down the fall, by persons who expect a trifle for the exhibition. It displays the resistless power of the element. The log, which is of gigantic dimensions, is tossed like a feather upon the surface of the water, and is borne to the foot almost in an instant. In Scotland, the falls of its rivers are seldom of great size; but the rocky beds over which they roar and dash in foam and spray – the dark, precipitous glens into which they rush – and the frequent wildness of the whole scenery around, are compensating features. The most remarkable instances are the Upper and Lower Falls of Foyers, near Loch Ness. At the upper fall, the river precipitates itself, at three leaps, down as many precipices, whose united depth is about 200 feet; but, at the lower, it makes a descent at once of 212 feet, and, after heavy rains, exhibits a grand appearance. The fall of the Rhine at Schaffhausen is only 70 feet; but the great mass of its waters, 450 feet in breadth, gives it an imposing character. The Teverone, near Tivoli, a comparatively small stream, is precipitated nearly 100 feet; and the Velino, near Terni, falls 300, which is generally considered the finest of the European cataracts. This “hell of waters,” as Byron calls it, is of artificial construction. A channel was dug by the Consul Carius Dentatus in the year 274 B. C., to convey the waters to