e
strata towards the centre, there forcing its way to the surface, if
the upper impervious beds be thin; or, if otherwise, remaining a
concealed reservoir, ready to yield its supplies to the shaft or
boring-rod of the well-sinker, and sometimes forming a living
fountain capable of rising many feet above the surface. It is in
this way that what are called Artesian wells are formed. The
following diagram represents such a disposition of the strata as
has just been referred to. The rain which falls on the tracts of
country at A and B, gradually percolates towards the centre of the
basin, where it may be made to give rise to an Artesian well, as at
C, by boring through the superincumbent mass of clay; or it may
force itself to the surface through the thinner part of the layer
of clay, as at D--there forming a spring, or swamp.

[Illustration: Fig. 8.]

"Again: the higher parts of hilly ground are sometimes composed of
very porous and absorbent strata, while the lower portions are more
impervious--the soil and subsoil being of a very stiff and
retentive description. In this case, the water collected by the
porous layers is prevented from finding a ready exit, when it
reaches the impervious layers, by the stiff surface-soil. The water
is by this means dammed up in some measure, and acquires a
considerable degree of pressure; and, forcing itself to the day at
various places, it forms those extensive "weeping"-banks which have
such an injurious effect upon many of our mountain-pastures. This
was the form of spring, or swamp, to the removal of which Elkington
principally turned his attention; and the following diagram, taken
from a description of his system of draining, will explain the
stratification and springs referred to, more clearly.

[Illustration: Fig. 9.]

"In some districts, where clay forms the staple of the soil, a bed
of sand or gravel, completely saturated with water, occurs at the
depth of a few feet from the surface, following all the undulations
of the country, and maintaining its position, in relation to the
surface, over considerable tracts, here and there pouring forth its
waters in a spring, or denoting its proximity, by the subaquatic
nature of the herbage. Such a configuration is represented in the
following diagram, whe