THE ARTESIAN WATER SUPPLY OF EASTERN FLORIDA.

lands, however, is very expensive and there is at present practically no demand for them.
Salt marsh: Extensive salt marshes occur along the Atlantic coast and bordering the streams entering the ocean.
UNDERGROUND WATER: GENERAL DISCUSSION.
'SOURCE.
Rainfall:-The chief source of underground water is the rainfall. Water vaporized through the energy of the sun passes into the atmosphere and is precipitated over the land as rain or condens. ed as dew or fog. The vapor is supplied to the atmosphere by evaporation, principally from the ocean, which, occupying three-foutihs of the earth's surface, is continuously exposed to the sun's rays. To the vapor from the ocean is added that arising from inland waters, from the dry land surface to the earth, and from the leaves of plants.
Small additions to the underground water supply may come through any one of a number of other possible sources, but the total amount thus added is relatively small and may be omitted in a general discussion.*
ANNUAL RAINFALL.
The annual rainfall is the measure of the column of water that would accumulate at any spot in the course of a year, if all that falls should be preserved. The measurement is commonly stated in inches. The average rainfall for the State as a whole for the fifteen years, from 1892 to 19o6, inclusive, as deduced from the U. S. Weather Reports, was 53.17 inches, annually. The year 1907 was a year of less than average rainfall, 49.15 inches, and if this year is included the average for the sixteen years, 1892 to 1907, falls below 53 inches, being 52.92 inches. If longer periods be considered the variation from this average is not sufficient to materially change the result.
The average rainfall at Jacksonville for the 33 years ending with 1904, was 53.21 inches, annually'; at Jupiter it was for the 17 years ending with 19o4, 59.19 inches annually. The area covered by this report lies in that part of the State supplied with
*A recent discussion of possible sources of underground water other than rainfall will be found in Bulletin 319, U. S. Geol. Surv., by M. L. Fuller.

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