AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 351 



outward, witliout fiudiug any tliorongb mixing up of different ingre- 

 dients, coming together from different directions of space — any mixing 

 up so tliorougli as to produce, even approximately, chemical homoge- 

 neousuess throughout every layer of equal density. Thus, we have no 

 difficulty in understanding how even the gaseous nebula, which at one 

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

 geneousness from which followed, by dynamical necessity, Europe, Asia, 

 Africa, America, Australia, Greenland and the Antarctic Continent, and 

 the Pacific, Atlantic, Indian and Arctic ocean depths, as we know 

 them at present. 



32. We may reasonably believe that a very slight degree of chemical 

 heterogeneousness could cause great differences ia the heaviness of the 

 snow shower of granules and crystals on different regions of the bottom 

 of the lava ocean when still 50 or 100 kilometers deep. Thus we can 

 quite see how it may have shoaled much more rapidly in some places 

 than in others. It is also interesting to consider that the solid granules 

 falling on the bottom may have been largely disturbed, blown as it 

 were into ridges (like rippled sand in the bed of a flowing stream or 

 like dry sand blown into sand hills by wind) by the eastward horizontal 

 motion which liquid descending in the equatorial regions must acquire, 

 relativ-ely to the bottom, in virtue of the earth's rotation. It is indeed 

 not improbable that this influence may have been largely effective in 

 producing the general configuration of the great ridges of the Andes 

 and Eocky Mountains and of the west coasts of Europe and Africa. 

 It seems, however, certain that the main determining cause of the 

 continents and ocean depths was chemical differences, perhaps very 

 slight differences, of the material in difierent parts of the great lava 

 ocean before consolidation. 



33. To fix our ideas let us now suppose that over some great areas, 

 such as those which have since become Asia, Euroije, Africa, Australia, 

 and America, the lava ocean had silted up to its surface, while in other 

 parts there still were depths ranging down to 40 kilometers at the 

 deepest. In a very short time, say, about twelve years according to 

 our former estimate (24), the Avhole lava ocean becomes silted up to its 

 surface. 



34. We have not time enough at present to think out all the compli- 

 cated actions, hydrostatic and thermodynamic, which must accompany 

 and follow after the cooling of the lava ocean surrounding our ideal 

 primitive continent. By a hurried view, however, of the affair we see 

 that in virtue of, let us say, 15 per cent shrinkage by freezing, the level 

 of the liquid must, at its greatest supposed depth, sink six kilometers 

 relativel}^ to the continents; and thus the liquid must recede from 

 them and their bounding coast lines must become enlarged. And just 

 as water runs out of a sand bank, drying when the sea recedes from it 

 on a falling tide, so rivulets of the mother liquor must run out from 

 the edges of the continents into the receding lava ocean. But, unlike 



