352 MAN AND THE GLACIAL PERIOD. 



since the withdrawal of the ice from the borders of these 

 old lakes : " The smooth surfaces are still scored with fine, 

 hair-like lines, and the eye fails to detect more than a 

 trace of disintegration that has taken place since the sur- 

 faces received their polish and striation. ... It seems 

 reasonable to conclude that in a severe climate like that 

 of the high Sierra it " (the polish) " could not remain un- 

 impaired for more than a few centuries at the most." * 



Europe does not seem to furnish so favourable oppor- 

 tunities as America for estimating the date of the Glacial 

 period ; still it is not altogether wanting in data bearing 

 upon the subject. 



Some of the caves in which palaeolithic implements 

 were found associated with the bones of extinct animals 

 in southern England contain floors of stalagmite which 

 have been thought by some to furnish a measure of the 

 time separating the deposits underneath from those above. 

 This is specially true in the case of Kent's Cavern, near 

 Torquay, which contains two floors of stalagmite, the 

 upper one almost continuous and varying in thickness 

 from sixteen inches to five feet, the lower one being in 

 places twelve feet thick, underneath which human imple- 

 ments were found. 



But it is difficult to determine the rate at which stalag- 

 mite accumulates. As is well known, this deposit is a 

 form of carbonate of lime, and accumulates when water 

 holding the substance in solution drops down upon the 

 surface, where it is partially evaporated. It then leaves a 

 thin film of the substance upon the floor. The rate of the 

 accumulation will depend upon both the degree to which 

 the water is saturated with the carbonate and upon the 

 quantity of the water which percolates through the roof 

 of the cavern. These factors are so variable, and so de- 



* See also Mr. ITpham in American Journal of Science, vol. xli, 

 pp. 41, 51. 



