7 02 THE POPULAR SCIENCE MONTHLY. 



tion from vapors. Oxygen and silicon, which doubtless composed 

 more than four-fifths of the entire bulk of the gases, were separated 

 from each other only by the elements that were needed to make up 

 the silicates. Their compound, silica, is involatile, and even infusible 

 by itself, under any degree of heat that we can command. The same 

 is true of lime and the earlier-formed silicates. Therefore it is impos- 

 sible to decide from their volatility which of these substances would 

 have first condensed and reached the surface. But, as the vapor of 

 silica, when formed, would still be of nearly the same specific gravity 

 with silicon (2.0*7), and would still separate by its immense volume 

 the oxygen from the calcium below, we may suppose that in any case 

 silica would have to be condensed and deposited, in greater part at 

 least, before lime, the oxide of calcium, could be formed. 



Along with silica were formed and deposited the silicates of alu- 

 mina — mica and feldspar ; then the partially fusible silicates of mag- 

 nesia, lime, and iron — hornblende, augite, and talc. There followed a 

 numerous order of complex silicates, in which the above-named ingre- 

 dients are varied by small proportions of manganese, soda, strontia, 

 zirconia, and many other mineral bases. With, and after these, was 

 produced the lime-deposit, the last of the minerals. The metallic 

 vapors, which were all heavier than the mineral, were condensed and 

 deposited chiefly during the later silicate period, and somewhat in the 

 inverse order of their volatility, but locally and irregularly as results 

 of great perturbations, or storms in the air. 



It will further be seen, from the last column of the table, that in 

 no respect are the materials of the earth deposited according to their 

 specific gravities as solids or liquids. There is, in the superincumbent 

 rock and ore masses, no order of position that would indicate in the 

 least the floating or buoyancy of the lighter substances. Therefore, 

 their arrangement cannot be referred to any origin from liquid con- 

 ditions ; and the only other theory is that of their gaseous origin. 



There are many apparent anomalies in the deposition of the metal- 

 lic and mineral compounds, which may require much study, and per- 

 haps further knowledge and experiment for their explanation. Thus 

 there is in one place a carbonate of lime — marble — and in another a sul- 

 phate of lime — gypsum. There are in certain localities sulphuret-ores 

 of iron or copper, and in others oxide-ores ; while the metals of great- 

 est vapor-density, as mercury, lead, bismuth, and antimony, are found 

 almost exclusively in sulphuret-ores. It will perhaps eventually be 

 established that sulphur was combined wholly into sulphuric-acid gas, 

 as carbon was formed entirely into carbonic-acid gas ; that both were 

 brought to the surface of the earth in solution with rain-water ; and 

 that sulphur in this form united with the metals which had failed to 

 be oxidized upon their condensation in the air, and sulphated the 

 quick-lime in the earth, which had not been carbonated by the car- 

 bonic solution. Then there is the exceptional production in Nature 



