THE ARTESIAN WATER SUPPLY OF EASTERN FLORIDA.

(i) Porosity of the material.
(2) Size of the pores in the water-bearing medium.
(3) Pressure.
(4) Temperature of the water.
(i) Rocks contain pores which, in the absence of a liquid, c,.e ordinarily filled with air. The relative proportion of these spaces in the rock to the whole volume is the measure of the porosity. Thus if a cubic foot of sandstone will hold in its pores onefourth cubic foot of water, its porosity is 25 per cent. The greater the porosity, the more water absorbed by the rocks.
(2,) The size of the pores in the rock affects the rate of flow. Rocks having large pores receive and conduct water many times more rapidly than those having small pores.
(3) The greater the pressure, other conditions remaining the same, the more rapid the flow. A pressure of one pound per square inch is required to support each 2.31 feet of a column of distilled water at the temperature *of 6o degrees F. The weight of watei from the deep zones is increased by solids in solution and in suspension, and is affected by changes in temperature. Something more than a hundred pounds pressure to the square inch is required to cause a flow from the bottom of a well 23I feet deep. Something nore than 500 pounds pressure to the square inch is required to. cause the rise of water in a boring a distance of I I50 feet. Pressure of this magnitude must materiallv assist in forcing water through the rock.
(4) The temperature of the water is found to influence the rate of flow. Slichter finds that a change from 5o to 6o degrees F. increases the capacity to transmit water under identical conditions by about 16 per cent.*
DEPTH OF UNDERGROUND WATER.
The limit of the downward extent -of water has not been reach-ed by borings or tunnels, some of which exceed a mile in depth. Water, while thus known to penetrate to a depth greater than a mile, probably does not reach beyond five or six miles at the most. The movement, as has been stated, is through natural openings in the rock. Pressure increases in the earth with depth, and it Is estimated that at a depth of approximately six miles, the pressureis so great that the pores and cavities of even the strongest rocks, are completely closed,t making it impossible for water to penetrate
*Water Supp~ly and Irrigation Paper, U. S. Geol. Surv. No. 140, p. 13, .2;3.i. M. Hoskins, I6th Ann. Rept. U. S. Geol. Surv., Part I, p. 859, 1896.

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