108 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
therefore, a flowing well; and of "artesian water," water under sufficient pressure to cause it to flow. With the extension into other areas of the use of deep wells as a source of water supply, many instances were found in which the water, although under pressure, and rising almost to the surface, would not flow. In some cases the water will flow ,in areas of low surface elevation, and yet fail to flow in a slightly elevated area near by. Artesian water thus came'to mean water under pressure causing it to rise in a boring when tapped, regardless of whether or not the pressure was sufficient to cause the water to rise above the surface level, and hence to flow. In the same way, and for similar reasons, the term 'artesian well' came to include not only flowing wells, but also, wells in which the water rises when the water-bearing stratum is tapped, regardless of whether or not the rise is sufficient to cause a flow. Occasionally, in popular usage, the term "artesian well" has been applied to any deep boring, and "artesian water," to water from such a well. In this report the term artesian is applied to water under pressure, and hence rising in a boring when tapped. The water may, or may not, rise to or above the surface. An "arrcsian well" is any well reaching to and tapping a stratum bearing such water; a "flowing well" is an "artesian well" that gives a surface flow. Artesian pressure is the pressure causing the water to rise in the boring when tapped. This is essentially the usage of these terms as adopted by the Division of Hydrology of the U. S. Geological Survey.*
CONDITIONS NECESSARY TO OBTAIN ARTESIAN
WATER.
As essentials for artesian .water it is necessary to have (I) an adequate source of water, and (2) the proper structural conditions to retain the water under hydrostatic or artesian pressure. L will be convenient to discuss first the structural conditions.
ARTESIAN BASIN.
A variety of 'conditions in the arrangement and structure of the underlying deposits may bring about artesian pressure. The simplest, although probably not the most common, is that of a basinlike arrangement of successive relatively previous and impervious strata. This typical structure, known as an artesian basin, is shown
*Water Supply and Irrigation Paper, U. S. Geological Survey No. i6o.