204 ON THE ORIGIN, MATERIALS, COMPOSITION, 



what did exist, and reasoned as indifferently when 

 they knew it, is true. The presence of water in 

 stones is so universal that I have never yet seen any 

 rock in which it was not found, when that could be 

 procured quickly from a sufficient depth. It is con- 

 tained even in granite and in the trap rocks ; and the 

 great change of colour and hardness which many of 

 the latter undergo after bejng formed into specimens, 

 is owing to its evaporation. Thus, specimens of au- 

 git rock, which have the waxy, soft look and green 

 colour of serpentine, when fresh broken, become 

 black in a few days. It was mentioned when treating 

 of the flexibility of rocks, that small granite veins 

 were sometimes found perfectly soft in the quarry ; 

 and these harden in a few days, apparently by the 

 evaporation of their water and the consequent preci- 

 pitation of silica, or else by the nearer approximation 

 of their parts. In Sky, as I formerly mentioned, I 

 have found masses of granular quartz, or sandstone, 

 which could be moulded by the hand when first taken 

 from the earth, but which, in the same manner, be- 

 came solid in a few days. In all these cases, the loss 

 of weight proves the presence of water, as it does the 

 porosity of the stones. Even the common quartz of 

 veins contains water under the same circumstances ; 

 losing both weight and transparency on drying, as I 

 have proved. The porosity of stones, as well as the 

 presence of water, are, thus, both demonstrated by 

 the same facts. But the former property ought 

 never to have admitted a doubt ; since the compact- 

 ness of flint and agate are apparently far greater than 

 that of any rock, compound or simple, and since 

 these, give passage to water, to oil, and to sulphuric 

 acid, as I have shown in an essay on this subject. 

 That the water in stones is actually saturated, with 





