54 FLORIDA GEOLOGICAL SURVEY—FOURTH ANNUAL REPORT. 
The chemical action of water is vastly more effective in the disin¬ 
tegration of rocks than the mechanical. Eocks consist ordinarily, 
as previously stated, of a mixture of minerals, and while all minerals 
are to some extent soluble, some are much more readily soluble than 
others. When these soluble minerals are removed in solution, the 
rock necessarily crumbles. Water is more' effective as a solvent 
beneath than above the surface. Kain water upon passing through 
the atmosphere and entering the earth, takes into solution more or 
less of the gases, carbon dioxide and oxygen. From the decaying 
vegetation in the earth it receives also various organic acids, all of 
which materially increase its solvent action. For this reason many 
rocks that are little affected by solution above ground are disinte¬ 
grated beneath the surface. 
Some chemical reactions in which water takes no actual part 
nevertheless take place much more readily in the presence of mois 
ture. This is particularly true in the process known as oxidation, 
which is a very important factor in the disintegration of rocks. Oxi¬ 
dation is the chemical reaction between the free oxj^gen of the air 
and various minerals in the rocks. This reaction, as previously 
stated, takes place much more readily in the presence of moisture, 
and slowly or not at all in the absence of moisture. The effect of oxi¬ 
dation is the formation of new minerals. Oxidation does not neces¬ 
sarily bring about decay, since the oxidized form of minerals is more 
stable than most other forms. Indirectly, however, it results in the 
breaking up of rocks. If, for instance, rocks exposed at the surface, 
contain sulphides, these on exposure are likely to be oxidized to 
oxides and the solidarity of the rock destroyed. 
Hydration is also an important chemical reaction accompanying 
decay of rocks. Hydration is the chemical reaction by which water 
is taken into chemical union by the mineral, thus forming in reality 
a new mineral. When hydrated a mineral is found to occupy more 
space than in the non-hydrated condition. Not all the minerals in fi 
rock as a rule are subject to hydration, but the increased space occu 
pied by the hydrated minerals results in the disintegration of the 
rock. 
The destructive effect of water in the form of ice sheets, although 
not effective in Florida, has been of importance in glaciated regions. 
Glaciers are found at the present time both in the arctic and in 
the antarctic regions, and in former times they were of greater 
extent. During the glacial period immense sheets of ice 
moved southward extending, in the central part of the 
United States, as far south as the Ohio Eiver Valley. The action 
