220 A. Tylor on Changes of the Sea- Level effected by 
the river is above that of the adjoining plains. 'The swampsand 
the numerous lakes formed by deserted river-bends communicate 
at all times of the year with the main stream. In these places 
mud could be constantly deposited mingled with the remains of 
the vegetation which grows Inxuriantly in the swamps. The only 
supply of inorganic matter for raising the level of the vast plains 
through which the river winds for hundreds of miles, must be 
the mud deposited upon them during the periodical floods. These 
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creased speed in the winter season favors itsremoval. The sv” 
mer deposit, however thin it may be, cannot occur without ¢oB- 
tracting the sizes of the channel. 
+ On this and the following points see First Report of the Tidal Harbors’ Com 
mission, above referred to, which contains the opinions of our most celebrated em 
gineers on the phenomena presented by tidal and other rivers. : 
Aes author has not met with any explanation of the causes that produces eo 2 
in cai oer ange the constant alterations taking place in them have ?° 
y to. 
