Cave itself (the largest of all), were eaten out of the solid mass of
limestone by the slow, patient, but irresistible action of acidulated
water."

Professor N.S. Shaler says: "The existence of deep caverns is a sign
that the region has long been above the sea."

Through the kindness of Professor C.J. Norwood, Chief Inspector and
Curator of the Geological Department of Kentucky, it is possible to
quote the first official report made on the caves of that state and
published in 1856, in Volume I., Kentucky Geological Survey Reports.
Dr. Norwood says: "Referring to the 'Subcarboniferous Limestone' (now
known as the St. Louis group of the Mississippian series), Dr. Owen
says: 'The southern belt of this formation is wonderfully cavernous,
especially in its upper beds, which being more argillaceous, and
impregnated with earths and alkalies, are disposed to produce salts,
which oozing through the pores of the stone effloresce on its surface,
and thus tend to disintegrate and scale off, independent of the solvent
effects of the carbonated water. Beneath overhanging ledges of
limestone, quantities of fine earthy rubbish can be seen, weathered off
from such causes. In these I have detected sulphate of lime, sulphate of
magnesia, nitrate of lime, and occasionally sulphate of soda. The
tendency which some calcareous rocks have to produce nitrate of lime is,
probably, one of the greatest causes of disintegration.'"

"Most extensive subterranean areas thus have been excavated or
undermined in Edmonson, Hart, Grayson, Butler, Logan, Todd, Christian
and Trig. In the vicinity of Green River, in the first of these
counties, the known avenues of the Mammoth Cave amount to two hundred
and twenty-three, the united length of the whole being estimated, by