AND ITS DELTA. 171 



but by its depth ; in which it is perhaps equal to any on the 

 globe; but is so contracted at the place of its entrance into the 

 ocean, as to be there less in width than it is found to be at a 

 thousand miles from its mouth ; the cause of this peculiarity is, 

 perhaps, not difficult to develope. The natural effect of rivers is 

 toencrease continually the depth and breadth of their beds, by 

 the perpetual abrasion of their waters; such must be the con- 

 sequence with regard to all rivers which do not supply by allu- 

 vion a sufficient quantity of matter to counteract this effect. Cer- 

 tain rivers, which in the upper part of their course pass through 

 fertile regions, whose rich and tender soil is easily broken 

 down and carried away by the impetuosity of the current, 

 not only supply this deficiency, but discharge such inconceiv- 

 able quantities of earthy matter, as to fill up, in a great measure, 

 those spacious bays and channels, scooped out by the hand of 

 nature, in order to facilitate the mingling of their waters with 

 those of the ocean; in such circumstances the breadth of the 

 river will always be in proportion to the mean quantity of 

 water discharged during the time it flows within its banks; for 

 it is to be remarked, that during the time of the inundation 

 the common channel of the river is in some measure lost in 

 the immensity of waters, which flow over its banks in all di- 

 rections; the bottom and sides of the channel, during this 

 time, suffer no abrasion, but, on the contrary, from the diminu- 

 tion of the velocity of the inferior currents, gain rapidly upon 

 the breadth of the river: the moment the current of the river 

 is confined within its proper banks, it begins to exert its do- 

 minion over its own channel, and fashions its bed by the mo- 

 mentum of its waters, attacking sometimes one side, sometimes 

 the other, according as the main filament of the stream is de- 

 flected from shore to shore; by which means large portions of 

 the newly-created soil are preserved, while in other situations (he 

 more compact earth is undermined and borne into the ocean, 

 and thus an equilibrium is restored between the channel and its 

 included waters; hence it comes to pass that rivers which run 

 through alluvial countries are much narrower in proportion to 

 the quantity of their waters, than those whose courses are over 

 rocks, gravel or sand; but on the other hand their depths 



