1U 



HI VERB. 



RIVERS. 



lie 



loe and half 



mil* wide, and in which the river U rapid, 

 U issues from thii valley by a narrow about two 

 r"t. hstirasa n IWuio and Faido, where a series of beautiful 

 alis occur, and the ravine is so narrow that au artificial mad hai 

 bwa eul <w Uw adjacent mountain oalld the Platifer. At Kni.l.. the 

 IVteo esAsn the middU valley of Leventina, in which it How* with 

 mat rapidity to (Uurnico. a durtanc* 1.1 al-ut tift.eii mil.-n, but 

 mthuiit 'f.TiiiinK any fall*. The valley i lee* than half a mile wide, 

 juj , . nteo the river enter* a 



dtort narrow, at th .mtlct from which it form* cataracts, and then 

 reaches toe wide valley oaUcd the Lower Valley of U-ventina, in which 

 Knows with a comparatively gentle course t Lago Magsiore, The 

 iMl.r number of the riven which originate in the Alps and Pyrenees 

 are at this letter dsecrlptinn The baniiw which occur in these river- 

 vllevs may at now remote period have been Blle<i with water, and 

 ilua may have baan drained off by the riven forming an outlet for 

 ih water, by the narrows which now connect their basins with one 

 another. 



A remaikat-le peculiarity of most of the rivers joining the Nil.-. 

 of OOUTM on the structure of the country through which 



(bey iuw, U that they have a circular, or rather a spiral course, so that 

 tiavfng described a curve of greater or less extent, round the 

 i msssrs which break the uniformity of the table- 

 laou of Abyssinia. they return upon themselves at a comparatively 

 hart distance fn.in thrir sources. As instances of this may be 

 nwnUuBnl the Mar.-!-, or KJior el Owh, the Bellegns, the Abai, the 

 *, the Uodjeb. 



me piacss the elevated mountain-ridges border immediately on 

 low plains. In such cases the riven cannot be said to have a middle 

 as soon as they reach the plain their character is changed, 

 he rapid torrent is converted into a gentle stream. Thus the 

 Maranon. after issuing from the 1'ongo de Hanneriche, and entering the 

 final plain. Hows slowly through the alluvial level ; and the Oaages, 

 after leaving the Himalaya Mountain*, at Hurdwar, flows with 

 great beuda through the immense plains of India. [HiM >TAX, in 

 UBOU. l'iv.| AU the riven which descend from the southern 

 f the Alps to the plain which the river Po traverses 

 are of the same description. In most cases, however, the 

 mountain -rrgion* are not in immediate contact with the plains, 

 but are separated from them by hilly tractx, anil that portion of 

 the ooorss of a river which lies through such a hilly region U called 

 Ui* uidJIt course. The rocky masses rarely approach the bed of a 

 river which has a middle course, but retire to nome distance from 

 them, so as to form between the higher grounds a wide valley, n hi. h 

 the inundations of the river have covered with a thick layer of alluvial 

 sail. It is remarkable that the highest ground of these valleys occurs, 

 without exception, on the very banks of the river*, and that the 

 land slopes from them towards the base of the higher p-..un.K 

 Accordingly the inundations generally cover the lower tracts, which 

 are at some "ti^tr from the river, to the depth of several feet, while 

 the banks are still above the surface of the water. The slop. 

 higher grounds, which may be considered as the outer banks of the 

 . because they fix a limit to its inundations, are generally gradual, 

 and covered with vegetation. The current of the river itself is gentle. 

 This change, when compared with that of the mountain stream, is 

 partly due to the more gentle descent of the hilly region, and partly to 

 the form of iU course. The bed of the river rarely lies in a straight 

 line, but continually forms bends, which are not acute angles, as in the 

 case of the luounUin-stmms, but have only a small curvature, so that 

 UM river runs through the valley in a serpentine course. This circum- 

 stance randan the course of the river much longer than it would be if 

 it flowed in a straight line, and consequently diminishes the fall and 

 the rapidity of the current 



It is observed that riven form numerous small islands and Band- 

 banks a short distance below the place where they issue from the 

 mountain region. Thus the Rhine, between Basel and Kehl, opposite 

 Stnsburg, and the Amazunas, below the Pongo de Manseriche as far 

 east as the mouth of the Yapura, and the Mississippi, between the 

 mouth of the St Peter river and that of the Missouri, form islands 

 and sand-banks. This is easily to be accounted for, by observing that 

 the river, on issuing from the mountains, retains a Urge quantity ol 

 earthy matter in suspension, which subsides when the current decreases 

 hi rapidity. This sediment forms islets and sand-banks. Though it 

 rarely happens, as already observed, that the rocky masses approach 

 close to the banks in the middle course of a river, yet this generally 

 occurs several times, and at such places the river usually forms rapids 

 and whirlpools. A ledge of rocks traverses the bed of the river in 

 some place*. Such ledges occur in the Danube at Pamau, near 

 Xeuburg above Vienna, near Presburg in Hungary above Perth, and at 

 Orsbova, or Orsova, on the boundary-line between Austria and Turkey 

 . Rhine they occur only between Mainz and Bonn, where the 

 river U traversed by three ledges, at Bingen, at St. Qaar, ami near 

 Andemach respectively. Such ledges are found in nearly all the largo 

 riven of Europe. The elevations by which they are produced are 

 sometimes connected with ranges of hills. 



Ledges of this description occur in many of the Atlantic rivers of 

 the United States, as the Potomac, the James River, and others ; anc 

 they mark with precision the passage of the riven from the undulating 



.r liillv region to the low plaina along the coast. There are of course 

 re] lids where these ledges occur. 



The 1'iieer course of rivers usually lies through a plain. In general 

 ilii-n- are no hill* which constitute* the outer margin of it* course, and 

 consequently there is no bottom or valley through which it runs. 

 The banks arc very little rained above the surface of the waters, and 

 the level ground extends to a greater distance. The current is s|n\v, 

 the fall being very small. Thus it was observed by l.i ('oiidaiuini', 

 that the Amazouas from the narrow at Obydos to its mouth, a 

 distance of 700 miles, docs not fall quite 12 feet, or little more than 

 0-2 of an inch per mile. It can hardly be conceived that a river with 

 so small a fall could propel its waters, and as the current of the 

 Amazouas is considerable, it can only be accounted for by suppo- 

 sing that the enormous volume of water which the river brings 

 down, drives on by its pressure that which is before it vmtil it 

 reaches the sea. [AMAZONAS, iu GEOG.I l)iv.] The surface of the 

 Elbe at Hamburg, about 70 miles from the North Sea, is not 

 more than 6 feet above the sea, and the fall per mile very little 

 exceeds an inch. The surface of the plain through which a river runs 

 generally consists of an alluvium, which the river has deposited during 

 the inundations. The matter of which this alluvium consists is soft 

 and loosely bound together, and consequently the current, slow as it 

 is, has power enough to remove a portion of the banks from on*' 

 and to deposit the detached matter on the other. Thus great changes 

 produced in the courses of rivers in the lapse of tune. Major 



Rennell surveyed a large portion of the lower course of the Ganges, 

 ami Ilia maps were very exact at the time. He also observed the 

 changes which the river had produced in its bed. About fifty years 

 afterwards the course of the Ganges was again surveyed, for the 

 mrpose of establishing a steam navigation, and it was found that the 

 nurse of the river Hardly in any place agreed with the maps of 

 {enncll. The most remarkable circumstance however is, that a river 

 requently divides into a number of arms, each of which rims to the 

 sea, though some branches re-unite and again detach themselves from 

 one another. Thus the Danube reaches the sea by seven arms, as the 



e formerly did, according to the ancient accounts, though there are 

 now only five arms in the Nile. Our best maps represent the number 

 of the mouths of the Ganges as amounting to ten at least. This 

 division of a river into several arms is easily understood when the soft 

 utiire of the alluvium is considered : and if we suppose that the river 

 n its operation of changing its bed, finds in its way a piece of t-oek or 

 other matter harder than the alluvial soil, by setting against such au 

 obstacle the current is divided, and flows on both sides of it : the 

 following inundation removes still more of the alluvium, and thus, in 

 course of time, a new arm is formed. 



The country which is enclosed by the arms of a river is called its 

 delta , from the form of the Greek letter A, which the delta of the Nile, 

 that which was best known to the ancients, greatly resembles : but the 

 term is generally appropriate, as most river deltas have that form. To 

 the base of the triangle, however, the deposit of matter brought down 

 by the river adds a curved projection seaward, rendering the entire 

 form of what is called the delta that of the sector of a circle. It 

 is a common conjecture that the space which is now occupied by tlie 

 delta of a river was once a part of the sea, which was filled np by the 

 d<5bris and earthy matter brought down by the river from the 

 mountainous and hilly country through which its upper and middle 

 course lie. This supposition is strongly supported by the nature of 

 the soil, which evidently consists of matter brought down by rivers, 

 and not of such as the sea leaves behind when, from any cause, it 

 retires. (On this subject see Captain Spratt's ' Investigation of the 

 Delta of the Nile,' as referred to in the article QUICKSANDS.) It may 

 be added, that this operation of rivers goes on during the inundations, 

 for after the waters have subsided the surface of a delta is found to be 

 covered with a very thin layer of mud, which soon becomes dry earth. 

 The deltas of rivers which are annually swollen by rains, which is the 

 case between the tropics, are generally much more extensive than those 

 which are formed by rivers whose inundations are only produced by 

 the melting of snow. 



There is a river of first-rate magnitude which has no delta, though 

 it seems to possess all those qualities which are supposed to. be 

 requisite to the formation of such an alluvial tract : the St. Lawrence 

 in North America reaches the sea by a kind of bay, which extends 

 upward of 300 miles, and gradually increases in width from three to 

 above one hundred miles. One would suppose that the form of this 

 bay would render it subject to be easily filled up by the earthy matter 

 brought down liy a river whose course exceeds 1800 miles; and yet 

 we do not find that an alluvium of any extent has been formed ale >ng 

 the banks of this wide cestuary, except on the right bank below 

 Quebec. This single instance might throw some doubt on the op 

 that delta* are formed by rivers in the way above mentioned, if the 

 peculiar nature of the St. Lawrence did not suggest an explanation of 

 this deviation from the common course of things, which rather con- 

 tinue than refutes the established principle. The St. Lawrence is the 

 only large river which traverses a great number of lakes. Even after 

 having left the five great Canadian lakes, it passes through those of 

 St. Francis, St. Louis, and St. Peter. In each of these lakes the 

 current ceases, and it is only perceptible where the river again issues 

 from the lake, AU the earthy matter therefore which the river 



