On Certain Cavities in Quartz, ^'c. 141 



not only proved by goniometrical measurement, but also by 

 placing a crystal of this spar into one of these depressions ; the 

 faces and angles of both come into exact apposition. This will 

 be apparent to you by making a drawing of a few crystals indis- 

 criminately taken up, viz. 



This form of carbonate of lime is of very frequent occurrence 

 in our neighborhood, and crystals, varying in size, are aggregated 

 together in masses corresponding to the cellular character of these 

 specimens. Still, in no specimen, have I been able to trace within 

 these cavities any of the remains of carbonate of lime. In other 

 specimens of cellular quartz, occurring in our vicinity, where the 

 cavities are formed by the disintegration of cubic and amorphous 

 pyrites, the remains of the sulphuret are quite evident. Would 

 it not, however, be fair to infer, from the exact correspondence of 

 the former with the latter, even though no portion of the former 

 remained, that the crystals of calcareous spar caused these cavi- 

 ties ? Assuming this inference as correct, we can now pursue 

 the inquiry further. 



In investigating the cause of this phenomenon, there are two 

 agents, water and heat, to which I shall confine my remarks ; 

 and as fluidity must have been essential to formations of such 

 peculiar character, it will be necessary first to ascertain what 

 natural operation could have contributed to it. We have only 

 to notice the frequent occurrence of siliceous stalactites, the 

 large beds of porcelain clay formed by the disintegration and 

 decomposition of granite, animal and vegetable petrifactions, the 

 formation of agates and other minerals in the cavities of basaltic 

 and trappean rocks, the constitution of sandstone, and many other 

 instances, to be convinced of the fact that water frequently holds 

 silex iii solution or suspension, and conducts it, by percolation, to 

 faults, dislocations, or crevices, where, becoming again precipi- 

 tated, it gradually consolidates into some regular mineralogical 

 form, or moulds itself to the particular contour and around the 



