228 THE CANADIAN NATURALIST. [May 



compounds at the centre became possible, those which were most 

 stable at the elevated temperature then prevailing, would be first 

 formed. Thus, for example, while compounds of oxygen with 

 mercury or even with hydrogen could not exist, oxides of silicon, 

 aluminium, calcium, magnesium, and iron might be formed and 

 condense in a liquid form at the centre of the globe. By pro- 

 gressive cooling, still other elements would be removed from the 

 gaseous mass, which would form the atmosphere of the non-gaseous 

 nucleus. We may suppose an arrangement of the condensed 

 matters at the centre according to their respective specific 

 gravities, and thus the fact that the density of the earth as a 

 whole is about twice the mean density of the matters which form 

 its solid surface may be explained. Metallic or metalloidal com- 

 pounds of elements, grouped differently from any compounds 

 known to us, and far more dense, may exist in the centre of the 

 earth. 



The process of combination and cooling having gone on until 

 those elements which are not volatile in the heat of our ordinary 

 furnaces were condensed into a liquid form, we may here inquire 

 what would be the result, upon the mass, of a further reduction of 

 temperature. It is generally assumed that in the cooling of a 

 liquid globe of mineral matter, congelation would commence at the 

 surface, as in the case of water ; but water offers an exception to most 

 other liquids, inasmuch as it is denser in the liquid than in the 

 solid form. Hence, ice floats on water, and freezing water becomes 

 covered with a layer of ice, which protects the liquid below. With 

 most other matters, however, and notably with the various mineral 

 and earthy compounds analogous to those which may be supposed 

 to have formed the fiery-fluid earth, numerous and careful experi- 

 ments show that the products of solidification are much denser 

 than the liquid mass; so that solidification would have commenced 

 at the centre, whose temperature would thus be the congealing 

 point of these liquid compounds. The important researches of 

 Hopkins and Fairbairn on the influence of pressure in augmenting 

 the melting point of such compounds as contract in solidifying, are 

 to be considered in this connection. 



It is with the superficial portions of the fused mineral mass of 

 the globe that we have now to do; since there is no good reason 

 for supposing that the deeply seated portions have intervened in 

 any direct manner in the production of the rocks which form the 

 superficial crust. This, at the time of its first solidification, 



