85 



so that the only measurement which affords any trustworthy 

 data for estimating the rate of increase is number 14. With 

 regard to this the only possible ground of error is the erosion 

 of the ofeneral surface of the solid limestone, of which the 

 roof is composed, by carbonic acid, since the year 1845, and 

 this is so small as to be practically inappreciable. We have 

 therefore evidence that the jockey's cap is growing at the 

 rate of '2946 of an inch per annum, and that if the present 

 rate of growth be continued it will finally arrive at the roof 

 in about 295 years. But even this comparatively short 

 lapse of time will probably be diminished by the growth of 

 a pendent stalactite above, that is now being formed in 

 place of that which measured ten inches in 1845, and has 

 since been accidentally destroyed. It is very possible that 

 the jockey cap may be the result not of the continuous but 

 of the intermittent drip of water containing a variable 

 quantity of carbonate of lime, and that, therefore, the 

 present rate of growth is not a measure of its past or future 

 condition. Its possible age in 1845 was estimated by Pro- 

 fessor Phillips at 259 years, on the supposition that the grain 

 of carbonate of lime in each pint was deposited. If, however, 

 it grew at its present rate it may be not more than one 

 hundred years old. All the stalagmites and stalactites in 

 the Ingleborough cave may not date fui-ther back than the 

 time of Edward III. if the Jockey cap be taken as a measure 

 of the rate of deposition. 



It is evident, from this instance of rapid accumulation, 

 that the value of a layer of stalagmite, in fixing the high 

 antiquity of deposits below it is comparatively little. The 

 layers, for instance, in Kent's Hole, which are generally 

 believed to have demanded a considerable lapse of time, 

 may possibly have been formed at the rate of a quarter of 

 an inch per annum, and the human bones which lie buried 

 under the stalagmite in the cave of Bruniquel are not for 

 that reason to be taken to be of vast antiquity. It may be 



