354 Of ^ ie Propagation of Heat 



lake would again become perfectly fresh. Should, how- 

 ever, the lake be so deep that the temperature at the 

 bottom should remain the same summer and winter, 

 without any sensible variation, it is most certain that its 

 waters there (at the bottom of the lake) would remain 

 perfectly saturated with salt forever. 



But are there not some reasons to conclude that the 

 water at the bottoms of all very deep lakes ought neces- 

 sarily to be salt, even in situations where there are no 

 mines of salt near ? 



The sea-shells that are frequently found in high inland 

 situations, as well as many other appearances noticed by 

 naturalists, strongly indicate that most of our continents 

 have been covered by the waters of the ocean. Now if 

 that event ever happened, however remote the period 

 may be at which it took place, it seems highly probable 

 that the salt water left at the bottoms of all deep lakes, 

 by the sea, on its retiring, must be there now. 



I cannot take my leave of this subject without just 

 observing, that the discovery of the impossibility of the 

 permanent existence of what we can plainly perceive 

 would be an evil certainly ought not to diminish our 

 admiration of the wisdom of the great Architect of the 

 Universe. 



