80 PREHISTORIC EUROPE. 



be not great, then the dissolution of the rock may not take place 

 so briskly as in another district where the percolating water, 

 although less acidulated, is yet more plentiful. 



Again, owing to differences of composition and structure, all 

 calcareous rocks are not equally acted upon by carbonated 

 water, some being more readily dissolved than others. Hence it 

 is evident that we cannot take the rate at which stalagmite 

 accretes in one particular cave as a standard of measurement by 

 which to judge of the time required for the accumulation of a 

 certain thickness of stalagmite in any other cave, unless we are 

 quite sure that the conditions are now and have for a long time 

 been the same in both, which it need hardly be said is never 

 likely to be the case. For instance, it is a well-known fact that, 

 owing to the humidity of our climate, marble monuments exposed 

 to the weather, especially in or near our manufacturing towns, 

 are very soon corroded ; while in other countries, with more favour- 

 able atmospheric conditions, the same stone may be subjected for 

 a much longer time to the action of the weather without showing 

 much appreciable wear. And if this be true of the calcareous 

 rocks exposed at the surface of the ground, it must also hold good 

 for the limestone, chalk, and marble that are buried below our 

 feet. Were the climate of Britain drier than it is, there can 

 be little doubt that our limestones would decay, and stalac- 

 tites and stalagmites would form, more slowly than they do at 

 present. But even under such conditions the calcareous rocks 

 would weather away, and stalagmites would accrete at very 

 diverse rates, owing, as I have said, partly to differences in the 

 quantity and quality of the percolating water, and partly also to 

 differences in the composition, porosity, and structure of the 

 limestones. Observations have put it beyond doubt that the 

 rate at which stalagmite increases is very variable. In some 

 instances the drip has taken many years to form a mere thin 

 glaze -the fraction of a line in thickness, while in one case 

 (Ingleborough Cave) a layer nearly a quarter of an inch in thick- 

 ness has accreted in one year. This latter, however, is probably 

 very exceptional. Had stalagmitic accretions generally increased 



