( 227 ) 



On the Mammoth Cave of Kentucky. By Professor B. SiLLl- 

 MAN Junior. From a Letter addressed to Professor Guyot^ 

 Cambridge^ dated Louisville^ November 8, 1850. 



At the level of the Ohio below the falls on which the city stands, 

 are found the lower beds of Silurian rocks and upper Devonian, the 

 eldest palaeozoic rocks to be seen in all this region. This city is 

 placed on a plateau elevated some seventy-five feet above the low 

 water mark of the Ohio, and the plain on which it stands represents 

 the general level of the surrounding country for a long distance 

 above and below. Mammoth Cave lies in a direction nearly south 

 of Louisville, on the Green River, and on the direct road to Nash- 

 ville, midway between Louisville and the latter city. Leaving Louis^ 

 ville, the stage road follows the main course of the Ohio, and generally 

 along its banks to the Salt River, some twenty miles ; crossing this 

 river the road bears south, leaving the Ohio on the right, and soon 

 enters a new region. By a gentle and easy ascent you continue to 

 rise for several miles by a circuitous path, passing in succession all 

 the members of the silurian, 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, interrupted only by the deep river beds, which are all very 

 nearly in 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 great extent of stiff red clays and unproductive 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 occupied its present place. Hence the idea so generally 

 accepted that the surface of the earth has fallen downward ; and this 

 is attributed to the wearing away of the rocks beneath by subterranean 

 rivers, or by some other mode of aqueous action. It is probable 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 abun- 

 dant 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 culti- 

 vation and by roads. These causes have obviously operated to furnish 



