ns Ee 3 : 
On Certain Cavities in que. Src. 141 
' not only proved «by gohiometrical 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 sawing of a few ore indis- 
apemee. 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 f been able to trace within 
these cavities any of the remains of carbonate of lime. In other 
ens 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 ee been essential to formations of souls? 
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 in 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 
