404 Lord Kelvin on the Formation of 
commences in the central region, by conglomeration into a 
granite of crystals descending through a vast surrounding 
lava ocean. The solid granite thus formed extends outwards 
till it comes to the surface. 
§ 16. The views regarding the solidification of the Earth, 
described in § 15, were first published in the Proceedings of 
the Victoria Institute, for 1897, in an article on " The Age 
of the Earth as an Abode fitted for Life/'' republished in the 
Phil. Mag., Jan., 1899. From this article the following 
passage is quoted : — " If the shoaling of the lava ocean up 
" to the surface had taken place everywhere at the same time, 
" the whole surface of the consistent solid would be the dead 
u 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 
a other parts could have sunk down to their present ocean 
" depths." 
§ 17. Our question is : — How can we explain why the 
Earth is not at present a mass of solid granite of approxi- 
mately spherical surface, deviating from sphericity just so 
much that, if it were covered with water, the water would 
be at the same depth in every part, when in equilibrium 
under the combined influence of gravitation and centrifugal 
force due to its diurnal rotation ? A possible, but it seems 
to me an almost infinitely improbable, explanation is that 
ocean depths are scars due to collisions with outside bodies, 
and mountain heights are due to matter left on the Earth 
by such collisions. When we look at the scarred surface 
of the Moon, we cannot but feel that it would be pushing- 
possibilities beyond the verge of absurdity to attribute the- 
geographical features of the Earth, and the corresponding 
features of the Moon, all to blows received by them, or 
matter shot down on them, from without. 
§ 18. After solidification, as described in § 15, contraction 
by loss of heat would almost certainly produce abundance of 
vertical cracks, proceeding inwards from all parts of the 
spherical surface (on the same dynamical principle as that 
which explains the well-known " crackling " seen on the glaze 
of many kinds of pottery). But there seems no possibility 
that the wide-spread hollows of the Antarctic, Pacific, 
Atlantic, and Indian Oceans, and the great areas of elevation 
in the continents, Europe and Asia, Africa, America, and 
Australia, and the seven to ten kilometre heights in the Andes 
and Himalayas, can have followed, by any natural causes, 
merely from the condition described in § 15. I have come 
to this conclusion after careful consideration of the dynamics 
