288 THE REVOLUTIONS OF THE CRUST OF THE EARTH. 



part of the volume of the earth, would be flattened if its rotation was 

 as rapid as that of the surface of our globe. This incontestable fact is 

 no proof against the supposition of a primitive fluidity ; it rather shows 

 us that the idea of fluidity is quite relative, for that which assumes a 

 certain form upon our earth may become level upou a globe where the 

 weight is greater. Spencer himself does not deny this fluidity, which is, 

 moreover, now generally admitted. 



At the commencement of the period at which we stopped in the his- 

 tory of our globe, the nucleus, composed of liquid and incandescent lava, 

 possessed a uniform very high temperature. A dense atmosphere sur- 

 rounded it, containing the elements of the present atmosphere, also sub- 

 stances not condensed, and all the water of the earth in a state of 

 vapor. This uniform temperature of the incandescent lava could not 

 continue indefinitely, for the liquids which were precipitated from the 

 upper strata of the atmosphere, where they were condensed by the cold, 

 decreased the heat by a new volatilization. This constant cooling of 

 the surface of the nucleus determined the first congealment of its 

 liquid mass. 



The scoria formed by this congelation were broken and heaped up by 

 the continual ebullition of the liquid sea of matter, by storms, which were 

 of a violence in proportion to tbe chemical- activity of the globe, and the 

 denseness of the atmosphere and by the tides, produced by the attrac- 

 tion of the sun and moon. Their debris collected into floating islands, 

 which were constantly increasing in extent and number, and at last by 

 their union formed the first, but still greatly-agitated, crust of the earth. 



Sir William Thorn son* has shown that the central heat can have no influ- 

 ence upon the temperature of the surface of the globe ten thousand years 

 after the definite formation of the terrestrial crust. This fact has its cause 

 in the want of conductibility of heat of the eruptive or plutonian rocks. 

 As an instance of this, one may walk with impunity upon a bed of lava, 

 a few days after an eruption, while at the depth of only a few feet the 

 lava is still incandescent, and so continues, sometimes for nearly a cen- 

 tury.t The thermal sources and the eruptions of lava may have main- 

 tained the temperature at a very high degree, even during more recent 

 times ; and it is probable that for three or four millions of years vege- 

 tation was affected by the high temperature of the soil whenever the 

 roots penetrated more than a yard below the surface.^ . 



As soon as the central heat ceased to act upon the temperature of the 

 surface of the globe and of the atmosphere, the precipitation of vapors 

 must have become almost general. The temperature of the first water 

 was undoubtedly high, on account of the great pressure of the atmos- 

 phere, of the heat liberated by condensation, and of the sensible influence 

 of the still recent crust. This high temperature of the water facilitated 



* Phil. Mag., January, 1863, ]>. 8. 



t L. Figuier, La Terre avant le Deluge, 1803, p. 35. 



t Thomson, Phil. Mag., January, 1863. 



