THE AGE OF THE EARTH. 2< 



cracks in the fiivst formed gTanite crust and through fresh 

 cracks in basaltic crust subsequently formed above it. 



Leibnitz's Consistentior Status. 



§ 30. When this oozing everywhere through fine cracks 

 in the surface ceases, we liave reached Leibnitz's consistentior 

 status; beginning with the surface cool and permanently 

 solid and the temperature increasing to 1150° 0. at 25 or 50 

 or 100 metres below the surface. 



Peobable Origin op Continents and Ocean Depths of 

 THE Earth (§§ 31-37.) 



§ 31. If the shcialing of the lava ocean up to the surface 

 had taken place everywhere at the same time, the whole sur- 

 face of the consistent solid would be the dead level of the 

 liquid lava all round, just before its depth became zero. On 

 this supposition there seems no possibility that our present- 

 day continents could have risen to their present heights, 

 and that the surface of the solid in its other parts could have 

 sunk down to their present ocean depths, during the twenty 

 or twenty-five million years which may have passed since the 

 consistentior status began or during any time however long. 

 Rejecting tlie extremely improbable hypothesis that the conti 

 nents were built up of meteoric matter tossed from without, 

 upon the already solidified earth, we have no other possible 

 alternative than that they are due to heterogeneousness iu 

 different parts of the liquid which constituted the earth before 

 its solidification. The hydrostatic equilibriuin of the rotating 

 liquid involved only homogeneousness in respect to density 

 over every level surface (that is to say, surface perpendicular 

 to the resultant of gravity and centrifu^-al force » : it required 

 no homogeneousness in respect to chemical composition. Con- 

 sidering the almost certain truth that the earth was built up of 

 meteorites falling together, we may follow in in)agination the 

 whole process of shrinking from gaseous nebula to liquid lava 

 and metals, and solidification of liquid from central regions 

 outwards, without finding any thorough mixing up of dif- 

 ferent ingredients, coming together from difterent directions 

 of space — any mixing up so thorough as to produce even 

 approximately chemical homogeneousness throughout every 

 layer of equal density. Thus we have no difficulty in under- 

 standing how even the gaseous nebula, which at one time 

 constituted the matter of our present earth, had in itself a 



