6 9 6 THE POPULAR SCIENCE MONTHLY. 



face of the earth, then all other materials of what is now the crust 

 must have been gases above it ; and, as nine-tenths of the elements in 

 vapor are heavier than oxygen — many of them more than ten times as 

 heavy — this gas could never have even touched this imaginary sea 

 of silicon. The oxidation, then, was only possible in the regions of 

 the atmosphere where oxygen existed and abounded. There only 

 among the free-moving gases could the incalculable amount of heat 

 evolved in the combination be carried off. 



We confidently assume, therefore, that the whole of this most 

 abundant mineral element once existed in the atmosphere in the form 

 of a high-heated gas ; and that some time and somewhere, on the con- 

 fines of the enormously-extended sphere of vapors, there was found a 

 current sufficiently cool to condense a portion of it. If the vapor of 

 silicon follows the general rule — that the density of gases is in propor- 

 tion to their atomic weights — then it was but a fraction heavier than 

 oxygen, and therefore not far below it in the atmospheric strata. The 

 unceasing commotion of the elements would soon have brought this 

 first cloud-mist of silicon into contact with oxygen, to which it has a 

 strong affinity under high heat. Oxidized, and in molten drops of 

 silica, or crystals of quartz, this new-formed material commenced its 

 descent toward the centre of gravity — the first creation from the pri- 

 mordial elements. As it fell into the more heated regions below, it 

 was probably soon evaporated, and, the vapor rising, carried up with 

 it the heat taken up in the evaporation. It was again condensed, its 

 heat given up, and it descended for another charge of the internal 

 fires. This, in all probability, is the epitome of the process of world- 

 cooling. 



At last, the showers of melted silex reached the liquid surface of 

 the nucleus, which the force of gravity and compression must have 

 formed, at an early period of the nebulous globe, of less or greater 

 extent about its centre. From this period the increasing torrents of 

 silica, intermingled with the silicates which were forming at the same 

 time, poured down through the heavy vapors, and filled up the fur- 

 longs-deep of granite ocean. On this vast deposit, and at about this 

 stage of the gradual cooling of the earth, began, we must suppose, the 

 first hardening and crusting over of the surface, since at this point, 

 near the close of the granite age, first commences the division of the 

 earth's crust into varieties and layers more or less distinct, as also the 

 upbearing of the heavy metals which, without this surface-hardening, 

 could never have floated on any molten sea of minerals. The slow 

 cooling of the granite masses beneath this crust and under the enor- 

 mous atmospheric or other superincumbent pressure, conformed them 

 to all the acknowledged conditions of the formation of the igneous 

 rocks. 



There is found in the different beds of the granitic rocks every 

 proportion of the admixture of silica with the silicates of alumina. 



