28 THE EIGHT HON. LOKD KELVIN, G.C.V.O., ON 



lietevogeneousness irom which followed by dynamical neces- 

 sity Europe, Asia, Africa, America, Australia, Greenhrnd 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 

 in 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 kilometres deep. Tlius we con cpiite s<^e 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 l)ottom, 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 l^lown into 

 saml-hills by wind) by the eastward horizontal motion 

 which liquid descending in the equatorial regions must 

 acquire, relatively to the bottom, in virtue of tlie 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 Rocky 

 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 difterences, of the material in different 

 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, 

 Ein-ope, Africa, Australia, and America, the lava, ocean had 

 silted up to its surface, while in other parts there still were 

 depths ranginv down to 40 kilometres at the deepest. In 

 a veiy short time, say about twelve years according to our 

 former estimate (§ 24) the whole lava ocean becomes silted 

 up to its surface 



§ 34. We have not time enough at present to thiidc out all 

 the complicated actions, hydrostatic and thermodynamic, 

 which must accompany, and follow after, the cooling of the 

 lava ocean surrounding oui- ideal primitive continent. By 

 a hurried view hcnvever 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 

 kilometres relatively 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 



