Mixture and Solution. 
125 
only rendered possible the accumulation of such great 
beds of ore, but oxidizised and destroyed the organic 
matters which in later ages appear in coal. 
There is just one matter that may be made clear 
at this point for the benefit of the general reader, and 
that is the difference — the great difference — between 
material held in suspension by water, and material 
held in solution . As a rule, matter held in suspension 
can be separated by filtration, while matter held in 
solution cannot be separated in this way. The finely- 
divided rock, that makes flooded rivers muddy, is held 
in suspension, and is not dissolved or in solution. If 
some fine sand is stirred up in a glass of water, we 
have a mixture. If a spoonful of salt is stirred up 
with water in the same way, we have a solution. Salt 
in solution disappears from view, and will not fall down 
on letting the water stand. Carbonated waters flow- 
ing in rapid torrents through limestone country affect 
the rock in two ways. The streams carry some of the 
finely ground-up limestone in suspension as a mere 
mixture of sand, or mud and water. But the water 
also dissolves a quantity of the limestone, which will 
appear again only by some chemical action, by being 
separated with the help of some living organism, 
or by the water drying up. The materials held in 
suspension will settle down partly on the speed of the 
current being arrested, and completely when the water 
comes to rest in a lake or lagoon. 
