64 



Fig. () represents the final state of the cavern. 



Fig. 6. 



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 



