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."

"The entrance to the cave, being thirty-eight feet lower than this bed
of limestone, is one hundred and ninety-four feet above Green River. In
the above two hundred and thirty-two feet there are several heavy masses
of sandstone, viz.: at one hundred and twenty-five, one hundred and
forty-five, one hundred and fifty, one hundred and sixty and two hundred
and fifteen feet, but it is probable that most of these have tumbled
from higher positions in the hill, as no alterations of sandstone have
been observed at these levels in the cave. From an elevation of from two
hundred and forty to two hundred and fifty feet, the prevalent rock is
sandstone without pebbles, which can be seen extending up to three
hundred and twelve feet to the foundation of the Cave Hotel. The united
thickness of the limestone beds on this part of Green River, is about
two hundred and thirty feet, capped with eighty feet of sandstone.
About midway of the section on this part of Green River, are limestones
of an obscure oolitic structure, but no true oolite was observed. Many
of these limestones are of such composition as to be acted on freely by
the elements of the atmosphere, which, in the form of nitric acid,
combine with the earthy and alkaline bases of calcareous rock, and give
rise to the formation of nitrates with the liberation of carbonic acid;