RIVERS. 



281 



The Susquehanna. 



inequalities, but many are formed by the arrest and gradual accretion of the alluvial 

 matter brought down by the waters. 



There is great diversity in the length of rivers, the force of their current, and the mass 

 and complexion of their waters ; but their peculiar character is obviously dependent upon 

 that of the country in which they are situated. As it is the property of water to follow 

 a descent, and the greatest descent that occurs in its way, the course of a river points 

 out generally the direction in which the land declines, and the degree of the declination 

 determines in part the velocity of its current, for the rapidity of a stream is influenced 

 both by its volume of water and the declivity of its channel. Hence one river often 

 pours its tide into another without causing any perceptible enlargement of its bed, the 

 additional waters being disposed of by the creation of a more rapid current, for large 

 masses of water travel with a swift and powerful impetus over nearly a level surface, 

 upon which smaller rivers would have only a languid flow. In general, the fall of the 

 great streams is much less than what would be supposed from a glance at their currents. 

 The rapid Rhine has only a descent of four feet in a mile between Schaffhausen and 

 Strasburg, and of two feet between the latter place and Schenckenschautz ; and the 

 mighty Amazon, whose collision with the tide of the Atlantic is of the most tremendous 

 description, falls but four yards in the last 700 miles of its course, or one-fourth of an 

 inch, in 1 J miles. In one part of its channel the Seine descends one foot in a mile ; 

 the Loire between Pouilly and Briare one foot in 7500, and between Briare and 

 Orleans one foot in 13,596; the Ganges, only nine inches ; and, for 400 miles from 

 its termination, the Paraguay has but a descent of one thirty-third of an inch in the 

 whole distance. The fall of rivers is very unequally distributed ; such, for instance, as the 

 difference of the Rhine below Cologne and above Strasburg. The greatest fall is com 

 monly experienced at their commencement, though there are some striking exceptions to 

 this. The whole descent of the Shannon from its source in Lough Allen to the sea, a dis 

 tance of 23-4 miles, is 146 feet, which is seven inches and a fraction in a mile, but it falls 

 97 feet in a distance of 15 miles between Killaloe and Limerick, and occupies the remaining 

 219 miles in descending 49 feet. When water has once received an impulse by following 

 a descent, the simple pressure of the particles upon each other is sufficient to keep it iu 



