s
weight presses toward the lowest level, always. The more water absorbs
of acid, the more powerfully does it attack and carry away the substance
of lime rocks through which it passes.

THE MAMMOTH CAVE OF KENTUCKY

There is no more fertile soil in the country than that of the famous
blue grass region of Kentucky. The surface soil rests upon a deep
foundation of limestone rocks, and very gradually the plant food locked
up in these underlying strata is pulled up to the surface by the soil
water, and greedily appropriated by the roots of the plants.

Part of the water of the abundant rainfall of this region soaks into the
layers of the lime rock, carrying various acids in solution which give
it power to dissolve the limestone particles, and thus to make its way
easily through comparatively porous rock to the very depths of the
earth. So it has come about that the surface of the earth is undermined.
Vast empty chambers have been carved by the patient work of trickling
water, which has carried away the lime that once formed solid and
continuous layers of the earth's crust. We must believe that the work
has taken thousands of years, at least, for no perceptible change has
come to these wonderful caves since the discovery and exploration of
them a century and more ago.

The streams that flow into the region of these caves disappear suddenly
into sink-holes and flow through caverns. After wearing away their
subterranean channels, leaping down from one level to another, forming
waterfalls and lakes, some emerge finally through hillsides in the form
of springs.

The cavern region of Kentucky covers eight thousand square miles. The
underground chambers found there are in the limestone rock which varies
from ten to four hundred feet in thickness, and averages a little less
than two hundred feet. Over this territory the number of sink-holes
average one hundred to the square mile; and the streams that have poured
their water into these basins have made a network of open caverns one
hundred thousand miles in length.

A great many small caverns have been thoroughly explored and are famous
for their beauty. The Diamond Cave is one of the most splendid, for it
is lined with walls and pillars of alabaster that sparkle in the
torchlight with crystals that look like veritable diamonds. Beautiful
springs and waterfalls are found in many caves, but the grandest of all
is the Mammoth Cave, beside which no other is counted worth