CHAPTER XIII.
THE PUNCH-BOWLS AND CAVERNS OF KENTUCKY.—"INTO THE UNKNOWN COUNTRY."
"This part of Kentucky borders a field of caverns that reaches from near the State of Tennessee to the Ohio River, and from the mouth of the Cumberland, eastward to and beyond the center of the State. This great area is of irregular outline, and as yet has been little explored. Underneath the surface are layers of limestone and sandstone rock, the deposits ranging from ten to one hundred and fifty feet in thickness, and often great masses of conglomerate appear. This conglomerate sometimes caps the ridges, and varies in thickness from a few feet only, to sixty, or even a hundred, feet. It is of a diversified character, sometimes largely composed of pebbles cemented together by iron ore into compact beds, while again it passes abruptly into gritty sandstone, or a fine-grained compact rock destitute of pebbles. Sometimes the conglomerate rests directly on the limestone, but in the section about us, more often argillaceous shales or veins of coal intervene, and occasionally inferior and superior layers of conglomerate are separated by a bed of coal. In addition, lead-bearing veins now and then crop up, the crystals of galena being disseminated through masses of fluorspar, calc-spar, limestone and clay, which fill fissures between tilted walls of limestone and hard quartzose sandstone. Valleys, hills, and mountains, grow out of this remarkable crust. Rivers and creeks flow through and under it in crevices, either directly upon the bedstone or over deposits of clay which underlie it. In some places, beds of coal or slate alternate with layers of the lime rock; in others, the interspace is clay and sand. Sometimes the depth of the several limestone and conglomerate deposits is great, and they are often honeycombed by innumerable transverse and diagonal spaces. Water drips have here and there washed out the more friable earth and stone, forming grottoes which are
