CHEMISTRY OF THE ROCKS. 59 



composition. There have been worlds made up apparently 

 without oxygen ; for the meteorites, which must be regarded as 

 sample specimens from some stranger world however they may 

 have been dispatched to us, are mostly composed of pure crystal- 

 line and malleable iron, which could have cooled into that con- 

 dition only where there was no oxygen nor carbonic gases. If 

 chlorine had been our superabundant gas, the silicon would per- 

 haps quite as readily have united with it, and formed as stable a 

 compound as with oxygen. But the product, instead of being 

 the hardest of rocks, would have been a liquid, very much re- 

 sembling water, a little heavier and nearly as volatile as the 

 common ethers. In this case there could have been no dry land, 

 and no living beings that we can conceive of. Eternal clouds 

 and storms would have covered the face of the surging and 

 boundless ocean. 



Hitherto in our accounts of terrestrial phenomena, water has 

 played no part. It is probable that it was early formed, and in 

 the condition of vapor or steam diffused through the upper air. 

 In this state it bears the highest degree of heat that we can produce, 

 without decomposition. Hydrogen is the lightest of all the gases, 

 and unquestionably took its place on the outer limits of the at- 

 mosphere. There it was brought into contact with oxygen by 

 the commotion of the elements, and converted into steam as fast 

 as its lowering temperature allowed of the combination. As we 

 might expect from the respective positions of the gases, all the 

 hydrogen which fell to the portion of the earth in the making 

 up of its constituents was transformed into water-vapor. Hydro- 

 gen is found in no other combination that cannot be traced 

 directly or indirectly to the decomposition of water. 



The aqueous vapor being thus formed and lying in the upper 

 and cooler regions of the air, it began after a time to condense 

 and fall toward the earth. Meeting with warmer strata as it de- 

 scended, it was soon evaporated and sent up with a load of heat 

 that was set free by a recondensatiori. Then another and perhaps 

 lower descent, for another charge of heat. Thus on the out- 

 skirts of the air, water-vapor was cooperating in the work of the 

 heavier vapors of the interior. It was the great fire-carrier of 



