50 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
had a part. The land surface when first elevated above sea was evidently much more nearly level than at present. Upon being lifted above sea level irregularities in topography rapidly develop.
A first step in. the process of erosion is the development of stream channels and valleys, largely through mechanical erosion. In addition to mechanical erosion, clusO n by solution due to underground water is likewise in process especially in sections underlaid by limestones.
As illustrating the efficiency of underground water as an eroding agent, the writer in a previous report computed the rate of erosion by solution in the sections of the state underlaid by limestones.* The estimate of the rate of solution given below is taken from that report.
Solution is the most apparent, and geologically the most important result of underground water circulation. Rain water, while passing through the air, takes into solution a small amount of C02 gas. To this is added organic and mineral acids taken up while passing through the soil. Increased pressure, as the water descends into the earth, enables the water to hold in solution greater quantities of gases, acids and salts, all of which greatly increase the dissolving power of the water.
That underground water is efficient as a solvent is evident from the analyses of well and spring waters. Rain water entering the earth with almost no solids in solution, returns to the surface through springs and wells with a load of mineral solids in solution determined by the length of time it has been in the ground, the distance traveled, and the character of the rocks and minerals with which it comes in contact.
The mineral matter thus taken into solution is carried along vith water, and, while some of it is re-deposited, a large amount is removed annually.
An estimate of the total mineral solids thus removed is difficult. A conception of the largeness of the amount removed is obtained from a consideration of some of the individual springs.
The water of Silver Springs contains, as shown by analysis, 274 parts solids per million parts water. Otherwise expressed, each m,1illion pounds of water is carrying with it 274 pounds of solids in solution. Silver Spring is estimated to flow a little more than three million pounds of water per minute (368,913 gallons). The interior of Florida is ,thus being carried into. the ocean through Silver Springs at the rate of more than 340 pounds per minute, or about six hundred tons: per day.
*Fla. Geol. Survey Bulletin No. I, pp. 46, 47, 48, 1908.