ON A PIECE OF TIMEEli ENCEUSTED WITH LIME. 93 



it may, I think, be averred that it is not palpably too high, but 

 is just as likely to be too low." 



'Now, in considering such a statement as the foregoing, it ap- 

 pears to me that ani/ equal rate of the formation of such calc-sinter 

 or stalagmitic covering of the rocky sides and floors of subterra- 

 nean caves is against, rather than favoured by, the facts of scien- 

 tific observation and inference. In ancient times, when the 

 surface of the ground over the cavities was covered with primae- 

 val forest, the ^'natural laboratory" was there at work in the 

 accumulation of decaying vegetation in the soil, '^ wherein the 

 rain would find the carbonic acid to act as a solvent upon the 

 calcareous earth." Hence the percolation through the soil of 

 the acidulous liquid and the drip into the caves, the origin of 

 the stalagmite, would be much greater, and produce greater re- 

 sults than could be possible under other and later conditions of 

 surface -ground, l^othing now covers Kent's Hole in Devonshire 

 but a little brushwood, and a row of houses now stands over the 

 stalagmite cave at Brixham. It seems undoubted, too, that the 

 material composing the stalagmite must have been decreasing 

 every year in the superjacent soil, besides the diminution of the 

 solvent every year that the operation was going on. Thus it 

 has been reckoned that the carbonate of lime, which now takes 

 two centuries to cover one-eighth of an inch (a greater deposit 

 having been formed in the Gunnerton Pit in eleven years) might, 

 in days gone by, have performed the work in a very few months. 

 At the rate of deposit of the stalagmite in Poole's Hole, near 

 Buxton, eight hundred years would have sufficed, instead of three 

 hundred and fifty thousand for the formation of the floorings of 

 Kent's Cavern. At the rate of that formed on the boards in the 

 Boltsburn lead mine, four thousand and eighty years would have 

 been the extreme time required for their deposition. 



In the case of the piece of timber recently encrusted with car- 

 bonate of lime in the Gunnei-ton Colliery, we may take tliree- 

 sixtcenths as its average thickness. It must be remembered, 

 however, that at, and even at some distance from, the bottom of 

 tlio shaft, the deposit on the boards, some of which are still /;/ 

 sitii, is ii^ore than a quarter of an inch. Thus three-sixteentlis, 



