On Certain Cavities4n Quartz, SjX. 143- 



It is in this way that I conceive the production of these celkilar 

 specimens may depend upon the agency of water ; but, as their 

 formation may be attributed, perhaps with equal propriety, to the 

 action of heat, I am disposed to carry the investigation a httle 

 further. 



Nearly all modern geologists and chemists have 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- 

 periments 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. S.o 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 conceivable that they could be effected by infiltration. 



