THE EAKTH. ilj 



Rivers thus set into motion are almost always found to mako 

 dicir own beds. Wliere they tind the bed elevated, they wear ils 

 substance away, and deposit the stdinient ia the next hollow, so 

 as 'in time to make the bottom of their channels even. Oa the 

 other hand, the water is contimuilly gnawing and eating away the 

 banks on each side ; and this with more force as the current hap- 

 pens to strike more directly against them. By these means it al- 

 ways has a tendency to render them more straight and parallel to 

 its own course. Thus it continues to rectify its banks and enlarge 

 Its bed ; and, consequently, to dimiiiish the force of its stream, 

 till there becomes an equilibrium between the iurce of the water, 

 a. id the resistance of its banks, upon which both will remain with- 

 out any further mutation. And it is happy for man tiiat bounds 

 are.thus put to the erosion of the earth by water ; and that we 

 had all rivers only dig and widen themselves but lo a certain 

 de^'ree."' 



Fn those plains ^ and large valleys where great rivers How, ll.c 



nviT of the Amazons has only ten ftet and a half of di-clivity upoii tw.i huu- 

 oreJ leag^ue.-i of extent of watf r, which makes -^j of an iiii'h for every JOl.0 

 feet. The Seine, between Valvins and Serves, bus only one ioot declivity out 

 of ikjOi). Xiie I^uire has, b.t veen Pouilly and Briare, one foot iu 7500 ;• but 

 between Briare, and Orleans only one foot in 13,596. lu East i'lizi-land, in 

 the United Provinces, two small neighbouring rivers liave, the one ^ of a.i 

 iiicii, the other ^ of declivity for evi-ry 1000 feet. The M,-.rwedo, between 

 Herdinxveld aud Dort, falls an iniii along- 1,125 f<jot; but between Dort 

 and the sea, only one inch along 9000 feet. Evea the most r;ipid rivers have 

 less declivity than is commonly imagined. The Ilhine between iicluiSiiaiiseu 

 and Stnusburgh has a fall of 4 feet in a mile ; and of 2 feet between Strasburgli 

 and Scheiikeiiacliaiitz. Hence we see the re^-son why one river may receive 

 another almost as large as itself, without any con»iJii nble eulargeineiit of its 

 bed ; the augmentation of its body only accelerates its coutte. Sometime; 

 one river falling into another with great rapidity, aud at a very acute aiigle, 

 will force the former to retrace its course and rtiuni for a sliortspace towards 

 its source. This i.as happened more than once to the Klione near Geneva ; 

 the irapttuous Arva, which descends from the mountains of Savoy, being 

 swollen bey.ir.d its u-iual size, has made the more genile waters of the Rhone 

 do w back into the lake of Geneva ; causing the wueels of the mills to revuUe 

 backwards. Some rivers have no stream whatever, and the cause is easily 

 discovered; the landh,iviiigscarcely any declivity, does not iinp;irt asufficieut- 

 ly strong impulse lo their waters, which are constantly rctaided, aud finally 

 atjsurbed by the sand. Sometimes these waters are evaporat-ed by tne heat 

 of the son, as is the case with the rivers of Anibia and ,\fi-ica; but they 

 mure commonly flow into pools, marshes, or salt lakes. 



1 Guglielmiui della N'atura de Fiumi, passim. 



2 jButtoa de Fleuves, passim, vol. ii. 



N 



