ON CAVES. 27 



Professor Hughes to Ingleborough at the time of the great storm, the effects 

 of which he has described, because a more accurate and valuable account of 

 that catastrophic incident could not have been furnished. The subject 

 is one of very great importance in many ways. The more we are struck 

 with the continuity of causation, the more must we guard against circum- 

 stances which carry the idea too far, especially in regard to questions 

 connected with chemistry, which afford abundant examples of the danger 

 of carrying this theory beyond its legitimate scope. We have many 

 examples of stalagmites forming with perfect regularity, and we assume 

 that the process has been going on from endless time. I have twice seen 

 the Ingleborough Cave. The first occasion was during a very wet summer, 

 when a vast deal of water came down, not in torrents, but with a very 

 rapid formation of stalagmite. The autumn following was very dry, and 

 the stalagmitic formation not so rapid, and I could not help thinking how 

 utterly impossible it must be to form anything like an accurate judgment 

 of the speed of formation when the process was shown to be going on at 

 two different rates. It is not merely the action of carbonic acid in the 

 destruction of the rock that strikes one, but the wonderful way in which 

 the solvent process goes on hollowing out the lime and disintegrating the 

 stone, until some flood occurs and washes away vast quantities of the broken 

 up debris. This is specially the case in the carbonated rocks, where you get 

 a more rapid solution than in other cases ; because the rock is honey- 

 combed and cut to pieces in a wonderful manner, so that it goes to pieces 

 with a comparatively small rush of water. Throughout the whole of this 

 question you must bear in mind that a very slight alteration in the balance, 

 whether of the carbonic acid produced by the surface vegetation, or in the 

 proportion of water to carbonic acid, may make a very wide difference in 

 the result. The presence of a little more or less silica in the water may 

 make a vast difference in the mode in which the travertine is deposited. 

 Any one who has had experience in connexion with steam boilers knows 

 full well that you may have it deposited in an exceedingly hard scale if 

 there be a sufficient amount of silica to cement it together ; or, if this is not 

 the case, it may exist as an exceedingly soft powder, which blows away 

 directly the blow-off cock of the boiler is opened ; in the same way it is 

 not merely the percentage of carbonate of lime that is dissolved and set 

 free by the evaporation of the carbonic acid, but whether there is sufficient 

 cementing action going on to form a solid mass to resist the inflow of the 

 water. One cannot help being struck with the amount of careful knowledge 

 displayed by the author of this paper. He goes back to the most minute 

 forms of things. This is what Lord Bacon did many years ago ; but the 

 lesson is one that has not been fully learned yet, although it is refreshing to 

 find that it has been acquired and put in practice by Professor Hughes. 



Sir WARINGTON W. SMYTH (taking up from the table a pipe encrusted 

 with stalagmitic^deposit) asked how long it had taken to produce that result. 

 I Professor HUGHES said he was unable to say. 



