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142 On Certain Cavities in Quartz, &. 
projecting points of the cavity. ‘The action of water, papers 
is capable of reducing-quartz to a fluid and plastic state. 
The occurrence of calcareous spar is most frequent in veins, 
cavities, or fissures, associated with quartz and other minerals. 
Its Seventies is likewise dependent upon the filtration of water, 
holding carbonate of lime in solution, which assumes its crystal- 
line character from the slow ‘percolation or evaporation of the 
water. Water, therefore, saturated with siliceous particles, in its — 
progress through the earth, will get access to cavities lined with 
calcareous spar, and here gradually precipitate them. These par- 
ticles will regularly accumulate, and as the water which conveyed 
. them there filters out, they will condense more and more, and ulti- 
sooty consolidate Ground the projections and within the angular 
sinuosities of the uneven surface of this mass of aggregated crys- 
tals: -'The quartz, thus becoming plastic, will mould itself to the 
spar, and this afterwards becoming dissipated by agents incapable 
of acting on the quartz, will leave its impressions accurately de- 
fined, and communicate to these specimens their peculiar char- 
acter. 
The question seisaiinie the separation of the carbonate of lime 
from the quartz next arises ; and the agent most likely to accom- 
plish this without impairing the integrity of the quartz or forming 
anew and insoluble compound in the cavities, I conceive is water. 
Although water itself is not a-good solvent of carbonate of lime, 
yet, when charged with carbonic acid, its power is much increased. 
Now, it is well known that there are many local sources of ‘ear- 
bonic acid gas, and even in. our own county, it is frequently 4 
found collected in large quantities in the bottoms of wells. - 
this gas, always generating by some subterranean process, com- 
bines readily with water in its vicinity, is evidenced by the fre-_ 
quent occurrence of carbonated springs: and as the absorbent 
power of the water is increased in a direct ratio with the pressure, 
so is its solvent power augmented in proportion to the aecumula- 
tion of carbonic. acid. Carbonic acid gas; therefore, confined 
within cavities beneath the surface of the earth, must necessarily 
be exposed to considerable pressure, and under these circumstances 
will be copiously absorbed by water in contact with it. Water; 
thus impregnated, being conveyed to the mass of crystals im- 
bedded within the quartz, will effectually dissolve it and wash it 
out from the cavities it formed, without in the least affecting the _ 
conformation of the quartz. 
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