10 PROCEEDINGS OF THE [Nov. 1859. 



Pbof. McCrady stated that in a recent visit to Tennessee he had visited some 

 caves in the neighbourhood of Clarkesville, in the game region as that of the 

 Mammoth Cave. One of .these caves especially exhibited the process by 

 which ^'sinks" are formed. This was evidenced at the very entrance which 

 was at the bottom of a large sink and consisted of a small hole in the ground 

 2ft. by 18in. at its narrowest part. This passage conducted through about 

 six feet of rock to the cieling of a large chamber, which he estimated at about 

 50ft. in height. Immediately below the narrow opening described above 

 was a hill which had to be descended before reaching the floor of the cavern, 

 and which he estimated at from 20 to 25 ft. in height. 



The sink had been formed evidently by the breaking in of the roof of the 

 cave and the hill beneath was simply the heap formed by the falling roof on 

 the cavern floor. But it was singular that the Cave ended abruptly in this di- 

 rection, so that in all probability the fallen mass was greater than sufficed 

 merely to form the hillock and that it had actually filled up the cave in 

 that direction. Further on, the floor of the cavern was covered by large an- 

 gular masses of rocks thrown together in the wildest confusion, so that footing 

 upon them in their slimy condition was really a laborious and dangerous 

 work ; especially when serious crevices had to be crossed. On looking up- 

 wards along the sidewalls of the cavern it was evident at a glance whence had 

 come the fragments in the floor. They were evidently the remains of succes- 

 sive roofs of the cave which had given way one after another leaving tneir 

 projectieg ledges still visible in horizontal lines along the cave wall. After 

 traversing this chamber or rather this long gallery, the character of the cave 

 changed, becoming narrow and low, and the cavity surrounded on all sides 

 with clay, clay walls, clay roof, clay floor. Suddenly the whole cave proved 

 to be shut up with clay except a narrow sinuous tunnel, admitting onlj' one 

 person at a time, and not much higher than the head. Through this he pass- 

 ed for about twenty paces when equally suddenly the clay barrier disappeared 

 and a wide but low roofed room again opened before him. A few paces futher 

 on the roof was of rock and so low that it could be readied with the candle 

 in his hand. It was also so much forced downwards by the superincum- 

 bent mass above as to have been cracked in the direction of the length of the 

 cave, so as +n present nearly the following transverse section, exhibiting the 



breaking down of an upper floor or roof in actual progress at A. Beyond 

 this as far as he went there were no signs of disturbance b^' the formation of 

 sinks. The low and breaking roof described above was followed by a large 

 high-roofed cavern with undisturbed stalagmites and stalactites, which in 

 one case had formed a large column from the roof to the floor. On the right 



