ON CAVES. 103 
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 stalagniitic 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 débris. 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 Warineron W, Suyru—(taking up from the table a pipe encrusted 
with stalagmitic deposit) asked how long it had taken to produce that result. 
Professor Hucues said he was unable to say. 
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