Lakes have been more numerous, €'c. ts 
muft not only be fteep, but its defcent muft alfo be 
continued. low@r than the bafon, otherwife the lake 
cannot be totally defaced. For when a ftream 
' takes up. a number of heavy bodies, it depofits them 
again as. foon as its velocity begins to diminifh; the 
largeft firft, and the-lefs in fucceffion, according to. 
their bulks and comparative weights. Hence it 
appears, that the lower parts of the channel are 
continually rifing from the acceffion of frefh mate- 
rials; and the upper end is gradually depreffed by 
the removal of the fame, till the whole becomes a 
gentle declivity, down which the current will glide, 
no longer capable of difturbing the impediments 
lying in its way: confequently, the form and 
dimenfions of its bed will become permanent. 
Now, if the lower mouth of a lake arrive at this 
fiate before it is fufficiently worn away, a part of 
its refervoir will for ever remain undrained, unlefs 
it happen to be deranged by violent caufes; or to 
be filled up with fand and pebbles brought from the 
adjacent country, by the rivers which flow into it. 
After thefe deftructive operations have ceafed of 
themfelves, there is reafon to apprehend, from what 
has been difcovered by Philofophers, that the fame 
procefs would be continued with equal certainty, 
though not with equal effect, for the conftituent 
particles of water are fufficiently hard to abrade 
the furfaces of very compact bodies; it having been 
proved by experiment, that the cohefion of glafs 
_ itfelf is not firong enough to refift their action. 
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