On the Mammioth Cave of Kentucky. 333 
lurian and the lower secondary, or the mountain limestone until 
at an elevation of 300 to 400 feet above the Ohio you reach the 
great upper plateau which stretches away for a long distance, in- 
terrupted only by the deep river beds, which are all very nearly 
on the same level with the Ohio. These upper plains are called 
the ‘Barrens,’ from the general sterility of the soil, which is 
formed to a considerable extent of stiff red clays and unproduc- 
tive sands, or of lime rocks lying near the surface. Everywhere 
in this upper country we are struck with the frequent occurrence 
of those circular holes or shallow pans which are called ‘sinks,’ 
from the popular belief that the surface has fallen away or sunk 
at some recent period. You see large trees standing dead in the 
water which fills these hollows, in a situation where of course 
they could not have grown supposing the water had long occu- 
pied its present place. Hence the idea so generally accepted that 
the surface of the earth has fallen downward, and this is attribu- 
ted to the wearing away of the rocks beneath by subterranean 
rivers or by some other mode of aqueous action. It is _prob- 
able that the hollows, already existing, are made water-tight by 
the cementing of the surface by fine mud floated by rains from 
the adjacent roads. I saw hollows of this sort standing full of 
Water in this very dry season, in which. the trees were not quite 
dead, while in others only the denuded. trunks were seen. From 
these stagnant pools arise the poisonous miasms that produce 
the fevers which are peculiarly abundant in those parts of the. 
Barrens where the sinks are most numerous. It is remarked that 
the ‘sinks’ have greatly increased in number, and the miasms in 
Virulence, since the country was opened by cultivation and by 
ro 
teen miles of Nashville the traveller again descends bysa similar > 
gradual declivity full 350 feet to the banks of the Cumberlan 
river, on which the city of Nashville stands. Here again the ob- 
server detects the oldest silurian rocks, compact blue crystalline 
limestones in which the fossils are almost obsolete, and unfossil- 
iferous sandstones, alternating with them. é : a a 
Mammoth Cave of Kentucky is situated in the midst of — 
level with the Ohio. . Dr. 
John Locke of Cincinnati has measured the depth of the cave 
barometrically, and is said to have determined it to bé 325 feet 
