LAKES. 99 



traces of ice were discernible in some of the shallows 

 near to its confluence with the sea, at the distance of 

 seven miles from the lake. 



But the same circumstances which render those deep 

 lakes difficult to be cooled, render them just as difficult 

 to be heated ; and thus the presence of a lake takes 

 the vicinity of it out of the extremes of chilling winter 

 and burning summer, which characterize northern coun- 

 tries, equalizes the temperature of the year, lengthens 

 the period of active vegetation, and clothes its banks 

 with a verdure unknown to any other places in the 

 same latitudes. Even the evaporation that takes place 

 from the surface of a lake which is surrounded by high 

 mountains, does not produce any thing like the same 

 degree of cold that is produced by evaporation from a 

 lake in a flat country. The air descends from the 

 mountains, is condensed in proportion to the depth to 

 which it descends, and being so, it is warmed. Another 

 thing : there is not the same difference of temperature 

 between the night and the day ; and thus there is less 

 dew and blight. In spring or autumn, the vegetation 

 around a marsh, or even a moist surface, is often found 

 destroyed, while on the banks of a lake not a leaf is 

 touched. 



But lakes in mountainous countries have another 

 advantage : they prevent those floods of the rivers, 

 which are so destructive where there are no lakes ; 

 and if they be in warm latitudes, they prevent the soil 

 from being burnt up and becoming desart. Rains fall 

 with greater violence upon varied surfaces than upon 

 plains, because there the atmosphere is subject to more 

 frequent and rapid changes ; the slopes of the surfaces 

 K 2 



