302 PHYSICAL GEOGRAPHY. 



from height to height into the valleys. He heard the voices of the waters as they leaped 

 from rock to rock. His imagination converted this external scenery into a picture of 

 the force of his adversities ; and hence the allusion, in the plaintive elegiac, commemo- 

 rative of his condition, to the " noise of cataracts," and to " deep calling unto deep." 



In advancing towards their termination, and at their embouchure, the great rivers 

 present several striking peculiarities. It has already been remarked, that a junction of 

 two large streams often occurs without any expansion of the surface of their waters being 

 the consequence, but a greater velocity of current and depth of channel. In some cases, 

 instead of a wider course being created by increased volume of water, there is actually a 

 narrower bed. Thus the Mississippi is a mile and a half wide, and the Missouri half a 

 mile wide, at their confluence, yet from that point to the mouth of the Ohio, the 

 medium width of the united rivers is but three quarters of a mile, and through the 

 lower parts of its course the main stream has, if any thing, a less surface-breadth, though 

 vast accessions are made to it by the Arkansas, Red River, and others of great depth and 

 body of water. Most of the tributaries of the Mississippi also are wider a thousand miles 

 apart from it than at the point of junction, and the same feature is characteristic of other 

 great streams, that as they increase their volume of water, and approach their termination, 

 they flow in narrower though deeper channels. The Nile is not so broad at Cairo as at 

 Siout, nor so broad at Siout as at Thebes. At Assouan, high up the stream, it is 3900 

 feet wide ; at Oudi, 36 miles above Cairo, it is 2900 ; and at Rosetta, near its mouth, but 

 1800. This is one of the many examples of benign adjustment with which the realms of 

 nature teem ; for hereby, a rich legacy of fertile soil, usually found at the mouths of 

 rivers, is saved from submergence, and becomes the inheritance of man. In their junction 

 with the sea, rivers display the diversity of sometimes pouring forth their waters through 

 a single mouth, and distributing 

 them into a variety of channels ; 

 circumstances mainly dependent 

 upon the country through which 



they flow being easily susceptible of excavation or not, 

 and upon the power of the stream. The Ganges pours 

 its flood through the many channels here represented. 



The Volga is celebrated for its seventy mouths ; and 

 the Ganges, the Nile, Mississippi, and Orinoco pour out 

 their current through several branches. The space 

 enclosed within these various channels is called a delta, 



from its triangular form, and general resemblance to the shape of the Greek letter A. So 

 powerfully do many of the great rivers rush into the ocean, that their waters are distinct 

 from those of the briny deep, when out of sight of the land. A British fleet lying opposite 

 to the mouth of the Rhone occasionally took up fresh water at a considerable distance from 

 the shore ; and Columbus found his vessel in the fresh water of the Orinoco before he dis- 

 covered the continent of South America. The collision of a great river current and the 

 opposing tide of the sea is sometimes so violent as to occasion an elevated ridge of 

 waters, heaving and tossing in a tremendous manner, shattering to pieces the ill- 

 fated vessel that comes into contact with it. The passage of the Garonne into the 

 Bay of Biscay, and of the Ganges into the Bay of Bengal, exhibit this phenomenon. 

 Upon the rivers meeting the advancing tides, a conflict ensues for the mastery, and 

 the force of the sea triumphing in the struggle, often sends a mountain-wave up the 

 streams, overturning boats, inundating the banks, and causing extensive destruction. 

 The most remarkable example of this struggle for empire, between the waters of the land 

 and of the deep, occurs off the mouth of the Amazon, and is the Indian pororoca. When 



