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 general 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 further 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 
