PLEISTOCENE CAVE-DEPOSITS. 81 



at this rate, all our caves ought to have been long ago filled up 

 with them. 



Obviously, therefore, no reliable conclusion can be drawn as 

 to the rate at which stalagmites have grown in caves generally, 

 from measuring the rate of growth in any particular cave at the 

 present time. To form an adequate conception of the age of a 

 given bed of stalagmite we ought to measure, if possible, the 

 rate at which that individual bed is now accreting. This, if it 

 be carefully determined, will not necessarily give us a perfectly 

 true result ; but when certain considerations, to be mentioned 

 presently, are kept in view, it will enable us to make some 

 approximation to that end. It is well known that during the 

 exploration of Kent's Cavern near Torquay a number of names 

 and dates, carved upon the uppermost bed of stalagmite, have 

 been detected, and some of these go back to the beginning of the 

 seventeenth century. Yet, as Mr. Pengelly tells us, " though 

 the stalagmitic matter has been continually accreting on them 

 ever since, it has been at so slow a rate that the inscriptions are 

 still perfectly legible." On the surface of a large boss of stalag- 

 mite which rises up from the general level of the floor, and thus 

 marks a spot where the drip has been more continuous, and the 

 growth, therefore, more rapid than in many other parts of the 

 cave, there is this inscription, " Eobert Hedges, of Ireland, Feb. 

 20, 1688." The film of stalagmite which has formed over it is 

 not more than the twentieth of an inch in thickness, nor have 

 we any direct evidence to show that the accretion of this parti- 

 cular boss was more rapid in earlier times. The bed of which 

 it forms a part is of very variable thickness, being hardly an 

 inch in some places, while in others it swells out to as much as 

 five feet. If, therefore, we took the rate at which the large boss 

 in question has accreted during the past two centuries as a 

 standard of measurement, we should infer that the upper layer 

 of stalagmite began to form about 240,000 years ago, while the 

 underlying layer, which occurs in the same cave and attains a 

 thickness of twelve feet, would at a similar rate require some 

 576,000 years for its growth. But these rates are certainly ex- 



G 



