302 Royal Society : — 



perforated by marine animals, and no traces of animal life or of human 

 art would present itself ; but on excavating the floor, both would be 

 found below the stalagmite ; whilst if the curious inquirer should 

 drive his pick into the roof, its fragments would bear testimony to 

 the same fact. 



Fig. 6 represents the final state of the cavern. 



That caverns are occasionally filled with water, and after remaining 

 full perhaps for centuries, are drained by artificial or natural causes, 

 is well known. A very interesting case presented itself to me when 

 visiting the caverns of Mitchelstown in Ireland. 



These caverns had recently (1833) become accessible, and were 

 then very imperfectly explored. I expressed to the guides my wish 

 to visit some of the unexplored portion, and, after traversing various 

 chambers during six hours, we entered a long and lofty cavern, the 

 floor of which sloped rather steeply towards one side. The whole 

 floor was covered with a coat of soft red mud, about three inches 

 thick, still holding a portion of the water in which it had been sus- 

 pended. No trace whatever of the footsteps of man or of animals 

 appeared ; the impression of our own feet alone marked the track 

 up to the point which we had reached. Being rather in advance of 

 my companions, my attention was suddenly attracted by what ap- 

 peared to me to be about a bushel of soot lying in a small heap on 

 the floor. On examination, I found it to consist of a moist spongy 

 substance, of a black colour, which might, if dry, have assumed the 

 form of a coarse black powder. Asking the opinion of my guide, he 

 suggested that it might have been the remains of a fire lighted by 

 some previous explorer ; but this was inadmissible. I looked round 

 for matter of the same kind, but on further search I could not 

 detect any other instance ; however, accidentally casting my eye 

 towards the roof of the cavern, I observed a black patch vertically 

 above the heap of supposed soot lying on the floor, and from 20 to 

 30 feet above it. The dotted line, a b, fig. 5, may repre- 

 sent the position. 



On my return from the cavern I examined the black sooty matter, 

 and found that it left but very small traces under the action of the 

 blowpipe. 



On the following day, having made inquiries as to the drainage of 

 the neighbouring country, I was informed that about twenty years 

 before my visit, a stream of water had been diverted from the valley 

 in which it originally flowed, into another adjacent valley. 



I then visited several quarries, in one of which, about a mile from 

 the caves, I observed a small stream of water terminating in a little 

 pool or sink. In this pool I noticed slight eddies, which occasionally 

 sucked in very small particles floating on the surface of the water. 



I now visited the valley from which the original stream had been 

 diverted, and found at some elevation a peat bog to which it had pro- 

 bably given rise. This peat was in several parts nearly black ; the most 

 decayed portion greatly resembled the black matter I had brought 

 from the cavern. The origin of this black matter in the cavern now 

 became apparent. 



