meunier: theory of volcanoes 639 



ginning of planetary history and to assume, with Laplace, that 

 the earth is but a drop of the chaotic substance separated from 

 the sun, like the other globules of the same nature, which, be- 

 fore or after it, have taken on the condition of autonomous 

 bodies. The sun represents the enormous residue of primordial 

 matter from which these successive products were derived. 



The globular form assumed by the mass that was to be our 

 planet results from the dominant property possessed by the 

 molecules of all mobile matter to attract one another and thus 

 to become grouped around their common center of gravity. La- 

 place has shown how this attraction causes the heating of the 

 whole mass and at the same time its general movement of rota- 

 tion around its own axis. We need add nothing to the concep- 

 tion of the author of the Exposition du Systeme du Monde in 

 order to understand in outline the successive stages of our globe, 

 all due to the spontaneous cooling caused by its position in 

 space, the temperature of which is far below that of the earth 

 itself. 



The first effect of cooling was to deprive the chaotic matter 

 of any homogeneity which it might have had at the start, the 

 result being a solid crust forming a partition between the un- 

 cooled fluids that constitute the nucleus of the globe and the far 

 less dense fluids forming the ocean and the atmosphere. 



Ever since the crust began to form and to grow thicker by 

 additions on the inside, owing to the progressive solidification 

 of the nucleus, it has tended to accommodate itself to the ever- 

 changing conditions arising from the steady diminution in vol- 

 ume of the enclosed mass. While that mass contracts during 

 cooling without changing its form, which remains spherical 

 while its diameter decreases, the crust, which is not contractile, 

 responds in a different way. As the support furnished by the 

 fluid nucleus is withdrawn because of its contraction, the crust 

 has to follow it and hence becomes increasingly corrugated, 

 with attendant faults (geoclases) and tangential thrusts. 



This is the well-known cause of topographic relief, the cause 

 of continents and oceanic basins. The water, instead of cover- 

 ing the globe as a uniform sheet, has collected in the oceanic 



