110 FLORIDA GEOLOGICAL SURVEY.-THIRD ANNUAL REPORT.
ing power of water acting along what was the coastal line at the time of formation of the strata under consideration. The coarser sand particles are dropped near the shore and form the sandstone; the finer sandgrains, together with more or less clay, are carried farther out, and form a finer grained sandstone grading ultimately
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Fig. 7.-Illustrating structures that may prevail in an artesian slope, a. a pervious water-bearing stratum which pinches out between impervious strata; b. a pervious water-bearing stratum which grades into a less pervious stratum; c. a pervious water-bearing stratum in which the artesian pressure is due merely to the friction of water moving through the pores of the rock.
into a clay. Similarly, a sandstone, or other pervious formation, may pinch out as a result of the thickening of a shale or clay bed. The term "artesian slope" has been applied to such an area to distinguish it from an artesian basin.
The friction of water threading its way long distances through the pores of an inclined pervious formation may result in an appreciable artesian pressure. That this is true, may be demonstrated by the following very simple experiment: Fill a tube of any length with sand, and incline at a convenient angle. The sand of the tube represents the pervious water-bearing stratum; the tube itself, the impervious confining strata. Let smaller tubes placed vertically be welded into the larger tube. These vertical tubes represent bored wells. The water will be found to rise in the vertical tubes, exhibiting an appreciable artesian pressure due to the friction of flow through the sand.
ARTESIAN WATER FROM UNCONFINED HORIZONTAL BEDS.
It is doubtless possible to obtain artesian water in some instances from unconfined horizontal beds. This condition is illustrated by the following sketch taken from the report of M. L.