12 FORMATION OF THE EARTH 



winds and counter trade-winds. It is possible that a ring like 

 that of Saturn is beginning to be outlined on its surface. The 

 existence of Saturn's ring is unquestionably connected with the 

 extreme lightness of the substances which constitute it and 

 which have yielded without resistance to the centrifugal 

 action arising from its rotation. The peculiar nature of these 

 distant planets and the fact that their birth goes back to so 

 distant a past that we can form no idea of it, prevents us from 

 being able to draw any very great profit from their study in 

 reconstituting the history of our globe. 



The gradual cooling of the Earth did not merely bring about 

 the separation of water from the atmosphere and its 

 condensation upon the surface. It led in course of time to a 

 whole series of modifications in the relations of the waters and 

 the solid crust. Undoubtedly the Earth at first was absolutely 

 spherical and was covered with a layer of water of probably 

 uniform depth. Air, water, and earth formed three concentric 

 spheres ; the solid terrestrial crust itself covering the central 

 mass, which remained burning and molten. The cooling 

 gradually disturbed the regularity of this geometrical arrange- 

 ment. Being homogeneous and contracting rapidly like all 

 liquids, the central mass would soon have separated itself from 

 the solid crust, and have left a void below, if the crust had not 

 been distorted so as to limit its capacity. 



The contraction of a cooling solid is, in fact, much slower 

 than that of a liquid, and the solid covering, for that reason, 

 would be unable to follow as quickly in its own contraction that 

 of the liquid mass which it covers ; it would collapse if it were 

 not distorted. Perhaps such a collapse occurred more than once 

 before distortion ; possibly both had taken place together. 

 This we shall probably never know, but it is of little importance. 

 Whatever really happened it can be shown by a very simple 

 geometrical calculation that, given equal surfaces, the solid 

 with the greatest volume is a sphere, while that whose volume 

 is smallest is a tetrahedron ; and therefore the crust, merely 

 through the process of cooling, must have tended to change 

 from a spherical form to that of a triangular pyramid with 

 four sides, whose four apices and the edges nearest to them 

 must have projected above the water. From that moment 

 continents and deep oceans must have existed. The sea, as the 

 Bible says, was separated from the dry land. At first sight it looks 



