and of the Phenomena of Volcanoes. 341 



only one substance, either simple or compound ; for it is not 

 likely that two distinct substances should pass into the state of 

 a liquid at exactly the same temperature. Upon being deposit- 

 ed in a mass, it would, by virtue of the mutual attraction of its 

 parts, assume the form of a sphere, and this sphere, if it were 

 thrown into a state of rotation, would naturally become in time 

 flattened at its poles. 



As the temperature of the- nebulous atmosphere surrounding 

 it continued to cool, another substance would become liquid, and 

 be deposited in a concentric bed around the former, and so the 

 process would continue until the most volatile alone of the con- 

 stituents of the nebulae remained in an elastic condition. 



We have hitherto overlooked the chemical actions which the 

 substances successively deposited might exert one upon the 

 other, and, leaving this out of the account, it would seem that 

 all these deposits having been the results of a slow and gradual 

 cooling, would be ranged round the central nucleus precisely in 

 the order of the temperatures at which they pass into a gaseous 

 condition. 



This, however, is not the mode in which the globe we inhabit 

 is constituted, and, in order to account for its actual structure, 

 we must next consider how this i-egular order would be interfered 

 with by the chemical affinities exerted amongst the constituents 

 of the several strata. 



Immediately upon the deposition of a new substance upon 

 one already formed, the chemical actions taking place at the 

 line of junction between the two may be presumed to give rise 

 to new combinations, and to occasion explosions, rendings asun- 

 der, and heavings up of the strata, an elevation of temperature 

 as a consequence of the intense chemical action excited, and a 

 formation of solid matter, whenever the new compounds result- 

 ing should require a temperature more elevated than that of the 

 previously existing constituents, lor continuing in a liquid con- 

 dition. It may therefore easily happen, that the internal beds 

 already solidified will return to a state of liquidity, and, where 

 the mass is considerable, a long period might elapse before the 

 centre, then less heated than the surface, is restored to an equi- 

 librium of temperatine with it. 



At the time when any one of these combinations was going 



