MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 5 



easy it is for small animals such as Crustacea and insects to be carried through these sink-holes 

 from the surface of the soil above into these caves. These sink-holes are said to average 100 to 

 the square mile, and Shaler claims that "there are at least 100,000 miles of open caverns beneath 

 the surface of the carboniferous limestone in Kentucky." He also (Antiquity of the Caverns, etc.) 

 claims that "there are at least 1,000 miles of open water channel beneath the surface of the 

 carboniferous limestone belt in Kentucky." 



Owen says : 



^he known avenues of Mammoth Cave amount to 223, and the united length of the whole equals 150 miles. 

 The average width is 7 yards, and the height the same. About 12,000,000 cubic yards of cavernous space have here 

 been excavated by calcareous waters and atmospheric vicissitudes. (Geol. Surv. of Kentucky, i, p. 81.) 



We will now avail ourselves of Mr. Stevens's description of Mammoth Cave, read at a meet- 

 ing of the Academy of Sciences, New York, adding some comments by Prof. J. S. Newberry : 



Mr. Stevens exhibited a geological map of Kentucky, showing the area of subcarboniferous limestone in which the 

 Mammoth Cave is situated. This is overlaid with a thin stratum, mostly of sandstone, that is pierced by thousands 

 of sink-holes, through which the surface drainage is carried down into limestone fissures and thus to the general 

 drainage level of the Green River. This stream passes at the distance of less than a mile from the Cave Hotel, the 

 floor of the latter being 312 feet above the water and 118 feet above the mouth of the cave. He briefly explained, 

 with a diagram, the general mode of cave production in limestone strata, showing that subterranean tunnels must 

 be started by the solvent action of slightly acidulated rain-water, and subsequently enlarged by erosion, along the 

 fissures in the limestone. These agencies are still at work in portions of the cave, and the whole of this limestone 

 country is thus honey-combed with caverns. No tunnel can thus be formed at any point lower than the general drain- 

 age level, since there must he an exit for the saturated water. The production of the fissures is referable to the gen- 

 eral upheaval of this area at the close of the coal period ; but that there has been subsidence since the completion 

 of much of the Mammoth Cave is indicated by the fact that at its lowest parts to-day the floor is covered with water 

 to the depth of 30 feet or more, having subterranean connection with Green River. The fissures intersect at 

 various angles, but many of them are nearly or quite coiucideut with the dip of the strata, which is very gentle. 

 Water passing through these forms the tunnels, while that passing through the vertical fissures scores out the pits 

 which pierce them. The same pit, starting from a sink-hole at the surface, may have successively lower tunnels as 

 exit passages. If the visitor encounters it while walking through the higher, and therefore older, tunnel, the upper 

 part appears to him as a dome, the lower as a pit. 



HORIZONTAL PROJECTION 



Fig. 2. 



VERTICAL PROJECTION 



Plan of Mammoth Cave after W. Le Conte-Stevmis. 



The rate of erosion in the Mammoth Cave has been variable. The older parts are perfectly dry and entirely free 

 from stalagmitic deposits, indicating rapid erosion, followed by elevation, so as to deviate the water completely into 

 other channels. In the newer parts the water is still dripping from the surface above and depositing stalactites and 

 stalagmites ; but as a whole the cave is by no means remarkable for these formations, being much surpassed in this 

 respect by the neighboring White's Cave, of more recent origin. Those which do occur are moreover deeply colored 

 with iron, which exists in the soil in the form of both oxide and sulphide. In the dry parts, the ceiling of the cave 

 is more or less covered with efflorescent calcic, magnesic, and sodic sulphates, which contrast with the iron- stained 



