122 FLORIDA GEOLOGICAL SURVEY SIXTH ANNUAL REPORT. 



bad 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 valle}^s, largely through mechanical erosion. In 

 addition to mechanical erosion, erosion by solution due to under- 

 ground water is likewise in process especially in sections underlaid 

 by limestones. 



As illustrating the efficiency of underground water as an erod- 

 ing agent, the writer in a previous report computed the rate of 

 erosion by solution in the sections of the state underlaid by lime- 

 stones.* The estimate of the rate of solution given below is taken 

 from that report. 



Solution is the most apparent, and geologically the most im- 

 portant result of underground water circulation. Rain water, while 

 passing through the air, takes into solution a small amount of 

 CO2 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 

 vvhich it comes in contact. 



The mineral matter thus taken into solution is carried along 

 with 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 

 nn'llion 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 Sil- 

 ver Springs at the rate of more than 890 pounds per minute, or 

 about six hundred tons per day. 



*Fla. Geol. Survey Bulletin No- i, pp. 46, 47, 48, 1908. 



