Lakes are of four distinct classes.
1. Those which have no streams of water running into nor
from them. They are generally very small, and of little
consequence.
2. Those which have streams flowing from them, but none
flowing into them. These are mostly supplied with water
from subterraneous springs. Some of this class form the
sources of large rivers, and are generally situated on
elevated land.
3. Those which have streams flowing both into and from
them. These, by a continual flow of fresh river water,
preserve their clearness and sweetness; and often, besides
the river which seems to flow through them, have sources
of their own near their shores, or from springs at their
bottoms.
4. The fourth class is ranked among the phenomena of
nature. They have no visible outlet, but receive the
waters of rivers which flow into them. The Caspian sea, in
Asia, is an instance of this kind. These lakes probably
lose the surplus of their waters by evaporation produced
by the heat of the sun.
The waters of lakes which receive their supply from springs and rivers,
partake of their qualities. There are some lakes whose waters are
exceedingly clear and transparent. Lake Wetter in Europe is so limpid
that a piece of money can be seen at the bottom at 120 feet depth.