4 



SCIENCE. 



ducted with much care, and the very best instruments 

 had been confided to him by the Director of the Win- 

 chester Observatory at New Haven. In August, 1881, 

 while the external temperature at the neighboring hotel 

 varied between 90 F. and 100° F., at points farther than 

 100 yards within the cave, the reading of the thermometer 

 was never more than 56 nor less than 52^°, the mean 

 temperature being 54 for the summer months. At a 

 point 1,000 yards within, a thermometer had been left for 

 six months, including the autumn and winter, and daily 

 visited by Mr. Klett, who reported the variation to be only 

 from 54 down to 53 . The underground temperature in 

 this latitude, for points 60 or 70 feet below the surface, is 

 usually assumed to be constant and about the same as 

 the mean annual temperature above. According to 

 Prof. Guyot's maps, the isotherm of 6o° passes about 

 thirty miles south of the Mammoth Cave, while that of 

 5o Q passes about forty miles north of Cincinnati. The 

 temperature of the Mammoth Cave is fully 6 lower than 

 has been commonly supposed, and may be taken as a 

 fair representation of that of the crust ot the earth in 

 the country immediately surrounding it. 



Mr. Stevens exhibited a geological map of Kentucky, 

 showing the area of sub-carboniferous 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 drain- 

 age 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 subter- 

 ranean 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 be thus formed at any 

 point lower than the general drainage level, since there 

 must be an exit for the saturated water. The production 

 of the fissures is referable to the general 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 thirty feet or more, having subterranean connection 

 with Green River. The fissures intersect at various an- 

 gles, but many of them are nearly or quite coincident 

 with the dip of the strata, which is very gentle. Water 

 passing through these forms the tunnels, while that pas- 

 sing 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 cider, tunnel, the upper 

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



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 com- 

 pletely 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 ot 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 limestone, giving rise to the 

 beautiful effects that have conferred celebrity on the open- 



ing known as the Star Chamber, and the myriad rock 

 flowers of Cleveland's Cabinet. 



The structure of the pits and domes was then illus- 

 trated with the aid of the accompanying map, by describ- 

 ing a journey through the cave. From the hotel, (a, fig- 

 ures 1 and 2,) the visitor walks to its mouth (b), by the 

 side of a shallow ravine, terminating in what was form- 

 erly a large sink-hole. The door of this fell through, 

 about seventy years ago, producing the present mouth of 

 the cave, and cutting off part of the gallery, now known 

 as Dixon's cave (c), which opens out near the Green 

 river, a half mile distant. A walk of 1000 yards brings 

 him to the Great Rotunda (d), about 170 feet in diam- 

 eter and 100 feet high. It is immediately under the 

 hotel, its roof being not more than 40 or 50 feet from the 

 surface. Besides the gallery, called the Narrows (b'), by 

 which access has just been obtained, another tunnel from 

 the further side terminates in the Rotunda, to which the 

 name of Audubon's avenue (b") has been given. The 

 large, almost hemispherical opening, seems to have been 

 cut out by the meeting of nearly opposite streams of 

 water, which found exit, probably, through the main 

 cave (e). At some distance within Audubon's avenue, 'a 

 small opening in the floor is found, connecting it with the 

 roof of the Mammoth Dome, a vast cavern 400 feet long, 

 100 feet wide and 250 feet high. These figures are of 

 course only approximate, but it is believed that they are 

 not exaggerated. Into this cavern the water is still trick- 

 ling, and stalagmites are forming with sufficient rapidity 

 to have cemented firmly to the floor a lamp dropped in 

 1812 and found in 1843. Returning to the Rotunda and 

 passing through a halt mile or more of the main cave, the 

 visitor reaches, at e , a large fallen slab of limestone to 

 which has been assigned the title of " The Giant's 

 Coffin." This makes the entrance to a side passage {g) 

 which leads off to the lowest part of the present cave. 

 The main cave forms an acute angle ( f) and may be fol- 

 lowed for several miles, terminating abruptly in a pile of 

 rocks, where the roof has fallen in the same manner as 

 at the terminus of Dixon's cave. Many of its side pas- 

 sages and avenues are yet unexplored. 



Returning and entering the side passage near the 

 Giant's Coffin the visitor passes obliquely beneath the 

 main cave, starting upon what is known distinctively as 

 the Long Route. At an expansion (h) are successive de- 

 posits ot gravel, sand and clay, indicating the downward 

 course of the water which was here partially arrested. 



