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On Certain Cavities in Quartz, §c. 143 
It is in this way that I conceive the production of these cellular 
specimens may depend upon the agency of water; but, as their 
formation may be attributed, perhaps with equal peopieiedyi to the 
action of heat, I am disposed to carry the oe a little 
further. ~ 
Nearly all modern geologists and chemists Keve given their 
consent to the existence of central heat, as indicated by the in- 
crease of temperature as we descend into the earth, by the heat 
of the water of the Artesian wells, by the occurrence of thermal 
springs, the existence of active volcanoes, and other familiar facts. 
That this central heat is very intense, may be inferred from the 
fused condition of volcanic productions, and yet it is questionable 
whether these productions are exposed to the maximum of heat. 
The volume and chemical character of lava would indicate vol- 
canic heat to be equally as great, if not much greater than that 
of the compound blowpipe, and yet we have seen, from the ex- 
periménts of yourself and Dr. Hare, that the power of the latter 
will fuse silex with ease and rapidity, and Lavoisier effected this 
with oxygen gas on burning charcoal. Now, as veins or beds of 
quartz are usually situated in primitive rocks, it must necessarily 
have been exposed to the most powerful action of central heat in 
order to occupy its present situation.* If, therefore, the cavities 
of these veins and fissures were pre-occupied and lined by crystals 
of calcareous spar, we can easily conceive how the injection of 
this siliceous fluid would cover and fill the angular points and de- 
pressions of the rhombic crystals, and by subsequent and gradual 
refrigeration the consolidation of the quartz would be effected, 
and one as it were be dove-tailed into the other. The heat, also, 
necessary to the fluidity of the quartz, would be more than suffi- 
cient to expel the carbonic acid from the spar, and as-this would 
not affect its crystalline conformation before the quartz would 
solidify, the cellular peculiarity of the latter would not of course 
in any wise be modified. - After these parts had sufficiently cooled, 
water gaining access to them, and coming in contact with the 
decarbonated lime, would cause it to slacken, thus producing per- 
fect disintegration ; and by the continuation of the supply of 
water, the hydrate of lime thus formed would be washed out of 
the cavities in the quartz. So that the same heat which rendered 
the quartz plastic enough to assume this form, prepared the cal 
* The igneous origin of these veins may, perhaps, be too positively ; inferred, as 
it is — that they could be effected by infiltration. 
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