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HUTTONIAN THEORY. 



357 





or folici flrata. In fuch cafes, it is evident, that 

 formerly the water muft have been much low- 

 er, as well as much higher, than its prefect level, 

 and this is only confiftent with the notion, that 

 the place was once occupied by a deep lake. 



318. If, following the light derived from thefe 

 indications, we go back to the time when the 

 river ran above the higheft of thofe levels at 

 which it has left any traces of its operations, we 

 fliall fee it compofed of a feries of lakes and ca- 



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tarads, from which, by the filling up of the one, 

 and the wearing down of the other, the water 

 have at length worked out to themfelves a quiet 

 and uninterrupted paiTage to the ocean. We 

 may, indeed, on good evidence, go back ftili 

 farther than the fucceffion of fuch meadows or 

 terraces, as are above mentioned, will carry us, 

 and may confider the whole valley, or trough of 

 the river, as produced by its own operations. 

 The original inequalities of the furface, and the 

 difpofition of the ftrata, muft no doubt have de- 

 termined the water-courfes at firft ; but this 

 does not hinder us from confidering the rivers as 

 having modified and changed thofe inequalities, 

 and as the proximate caufes of the fliape and con- 

 figuration which the furface has now aillimed. 



319. From this gradual change of lakes into 

 'ivers, it follows, that a lake i.s but a temporary 



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. jjjjtef'^ i and accidental condition of a river, Avhich is 



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