PLEISTOCENE CAVE-DEPOSITS. 79 



lations furnish as to the prolonged duration of the Old Stone 

 Age. I have mentioned the fact that frequently the floors of 

 the great limestone-caverns are paved with a material called 

 stalagmite, in and underneath which the relics of Palaeolithic 

 man and his congeners are often met with in abundance. The 

 general appearance of this deposit must be familiar to most. It 

 is a carbonate of lime which may be loose and friable in texture, 

 or harder and more coherent, but in many cases it is dense and 

 crystalline. It varies also in colour from creamy white to 

 yellow and red, being stained by the oxides of iron and vegetable 

 matter. The mode of its formation is very simple. Eain- water 

 invariably contains some proportion of carbonic acid, and as it 

 sinks through the soil, which is often enough charged with 

 decaying organic matter, it may take up more before it reaches 

 the underlying rocks. Such acidulated water filtering down- 

 wards into the cracks and crevices that seam a bed of lime- 

 stone, immediately attacks the rock, and carries away a certain 

 portion in solution. By and by the now calcareous water oozes 

 out on the roof of a cave, where as the drops gather and fall 

 they are of course subject to evaporation. Thin shells or pel- 

 licles are thus deposited on the roof, and corresponding accre- 

 tions form on the floor. By the continual prolongation of the 

 tiny shells from above long pendent stalactites are formed, while 

 cakes and rounded bosses, domes and mammillated heaps, grow 

 upwards, as it were, from the ground. If this process goes on 

 uninterruptedly, the time comes when the stalactites and stalag- 

 mites meet, so as to form fantastic pillars reaching continuously 

 from floor to ceiling. 



In most cases these calcareous accretions are of slow growth, 

 an inch or two requiring, as a rule, many years for their forma- 

 tion, but sometimes they form more rapidly. A good deal 

 depends upon the quantity and quality of the percolating 

 water, and also upon the character of the limestone. Where 

 the soil is well charged with organic matter, the water that 

 finds its way down into the rocks being highly acidulated will 

 dissolve limestone rapidly. But if the rainfall in such a case 



