this vertical section of the cave, where
he is likely to find himself delivered in a pool of water of no great
depth, the bottom of which is occupied by a quantity of small, hard
stones of a flinty nature, which have evidently come from the upper
parts of the cavern. The close observer will have noted that here and
there in the limestone there are flinty bits, such as those which he
finds in the pool. From the bottom of the dome a determined inquirer
can often make his way along the galleries which lead from that level,
though it may be after a journey of miles to the point where he
emerges from the cavern on the banks of an open-air river.

Although a journey by way of the sink holes through a cavern system is
to be commended for the reason that it is the course of the caverning
waters, it is, on the whole, best to approach the cave through their
exits along the banks of a stream or through the chance openings which
are here and there made by the falling in of their roofs. One
advantage of this cavity of entrance is that we can thus approach the
cavern in times of heavy rain when the processes which lead to their
construction are in full activity. Coming in this way to one of the
domes formed beneath a sink hole, we may observe in rainy weather that
the water falling down the deep shaft strikes the bottom with great
force; in many of the Kentucky caves it falls from a greater height
than Niagara. At such times the stones in the basin at the bottom of
the shaft are vigorously whirled about, and in their motion they cut
the rocks in the bottom of the basin--in fact, this cavity is a great
pot hole, like those at the base of open-air cascades. It is now easy
to interpret the general principles which determine the architecture
of the cavern realm.

When it first enters the earth all the work which the water does in
the initial steps of cavern formation is effected by solution. As the
crevice enlarges and deepens, the stream acquires velocity, and begins
to use the bits of hard rock in boring. It works downward in this way
by the mixed mechanical and chemical action until it encounters a hard
layer. Then the water creeps horizontally through the soft stratum,
doing most of its work by solution, until it finds a crevice in the
floor through which it can excavate farther in the downward direction;
so it goes on in the manner of steps until it burrows channels to the
open stream. In time the vertical fall under the sink hole