CHEMISTRY OF THE KOCKS. 61 



burnt or unburnt, before air-breathing life could come to any 

 perfection. The solidifying of the carbonic oxide was the latest 

 and slowest of the atmospheric changes. 



It appears that during the epoch of the hydration of the lime- 

 rocks there occurred periods when the waters were gathered into 

 seas, and were sufficiently cooled for the existence of marine in- 

 fusoria, mollusks, and corals. Life in some form has been ever 

 ready to spring into being the moment that conditions and sur- 

 roundings were suitable for it. After the deposition in those 

 temporary oceans of considerable thicknesses of Cambrian or 

 Silurian strata mixed with organic remains, some rent or uphea- 

 val has let the waters down to new beds of unslacked material, 

 which have heated and as it is termed metamorphosed those 

 first fossil if erous deposits. 



The subsequent changes which the earth's crust has undergone 

 aqueous, volcanic, and organic the working up of the con- 

 glomerates arid sandstones, the depositing of the deep-sea beds, 

 the overflowing of the traps and lavas, the storing away of the 

 carboniferous treasures, are all the story of every hand-book of 

 geology, and pertain no more to one theory than another of the 

 origin of the rocks. When the quarries of the igneous rocks 

 were once made and opened up to aqueous operations, the after- 

 work was merely mechanics and masonry. 



We have heretofore assumed that the gases which originally 

 composed the aerial envelope of the earth, took up separate posi- 

 tions therein according to their specific gravities. This might seem 

 to be controverted by experiments on the diffusion of gases, in 

 which those of very different weights, as chlorine and hydrogen, 

 will intimately commingle, even against gravity, when brought 

 into contact. This may be true in the narrow compass of lab- 

 oratory experiments, and yet not apply to any considerable thick- 

 nesses of the gases. Such a diffusion of one mile in depth of 

 chlorine would be equal to lifting up to the hydrogen a shell of 

 solid iron two feet thick. Whether we explain the distinguishing 

 principle of the constitution of gases as a mutual repulsion of 

 their moleciiles, or according to a late theory, as an incessant 

 motion and clashing of atoms, there is nothing in either to warrant 



