142 
FLORIDA STATE} GEOLOGICAL SURVEY. 
ARTESIAN SLOPE. 
The basin arrangement of strata is not the only possible struc¬ 
ture resulting in artesian pressure. The same result may, among 
other ways, be brought about quite effectively by an inclined 
porous stratum wedging out between two impervious strata. This 
condition is illustrated by the accompanying simple sketch, in 
which the pervious stratum (a) is represented as pinching out 
and disappearing between impervious strata. A pervious stratum 
grading into an impervious, or less pervious condition resulting 
Fig. 2.—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 pervi¬ 
ous 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. 
in artesian pressure, is represented by (b) of the same drawing. 
These conditions are often met with in the strata of the coastal 
plain. Not infrequently, a sandstone formation grades off shore 
Into a finer sandstone, and ultimately into a shale. This condition 
comes about naturally through the sorting power of w r ater 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 sand- 
grains, together with more or less clay, are carried farther out, 
