THE WORLD BEFORE LIFE. 519 



history of the earth at this early period was, therefore, merged in that 

 of the solar system. 



The centrifugal force produced by rotation would cause rings of 

 gaseous matter to separate themselves one after another from the cen- 

 tral mass, the latter turning on its axis more rapidly after the removal 

 of the exterior. The separated ring would then have been an annular 

 nebula. As many as six rings must have been cooled before the earth- 

 mass separated itself from the interior sphere carrying the substance 

 of the sun, and the inferior planets. 



The next stage of growth would naturally consist in the breaking 

 up of each ring by itself, perhaps in consequence of inequalities in dif- 

 ferent parts, and condensation into a sphere of greater specific gravity. 

 The falling of the particles would add heat, and perhaps quickly in- 

 duce the fluidity of the mass. While still gaseous, other rings may 

 fly off, to become satellites. All the nebulae, by constant rotation, 

 may have given freedom to the contained particles to arrange them- 

 selves according to their relative densities, the heaviest atoms falling 

 to the centre, and the lightest remaining at the surface. The process 

 of reparation into zones must have been analogous to the cooling of 

 liquids. As fast as their superior density caused particles to descend, 

 the lighter atoms would be displaced and sent to the surface, either 

 to be cooled, 6r to remain permanently in a higher stratum. But, at 

 the close of this period, there must have been, outside of the fluid, an 

 enormous thickness of gases which did not liquefy till after the crust 

 had formed to a considerable amount. 



Period op Igneous Fluidity. — At the commencement of this 

 period the earth seems to have been a flattened sphere, composed of 

 melted matter like lava, encircled by steam and easily-volatilized 

 liquids and solids, but girdled externally by an atmosphere ; rotating 

 upon its axis and revolving round the central sun. It was a sun of 

 itself, emitting light and heat, thus forbidding the distinction of day 

 and night, though the planetary movements inducing the alternations 

 of position were as well marked as now. The several compounds 

 constituting the material of the earth were probably arranged in con- 

 centric zones according to their relative gravities, just as we now ob- 

 serve the settlings in a copper or iron furnace. A general mixture of 

 rich and poor ores, fluxes and fuel, is put into the receiving-vault ; 

 when ignited, the solids mix together, melt into a fluid, the heavier 

 metals sinking to the bottom, and the slags rising to the surface to be 

 skimmed off. So the metals would naturally gravitate to the centre 

 of the fluid earth, and around them might be several zones of succes- 

 sively lighter compounds, the exterior being the least heavy of all, and 

 answering to the slags of the furnace. The specific gravity of the 

 whole earth is now 5.65, when compared with water, as determined 

 from astronomical sources ; but that of the surface-rocks is less than 

 half this amount : hence we have abundant reason to believe that the 



