“Rain-water, falling amid leaves and grass, and sinking into the soil, absorbs large quantities of carbonic acid.  On reaching the underlying limestone, the latter is instantly attacked by the acidulated water in which it is dissolved and carried away.

“It is agreed among geologists, amazing as the statement may seem, that the immense caverns of Virginia, Kentucky and Indiana, including Mammoth 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 those best acquainted with the Cave, at one hundred and fifty miles; say that the average width and height of these passages amount to seven yards each way, which is perhaps near the truth; this would give upwards of twelve million cubic yards of cavernous space which has been excavated through the agency of calcareous waters and atmospheric vicissitudes.”

Page 169:  “On the south side of Green River the platform of limestone forming the descent into Mammoth Cave is two hundred and thirty-two feet above Green River.”