A HISTORY OF SCIENCE 



Plutonists claimed as of igneous origin. This conten- 

 tion had the theoretical support of the nebular hy- 

 pothesis, then gaining ground, which supposed the 

 earth to be a cooling globe. The Plutonists laid great 

 stress, too, on the observed fact that the temperature 

 of the earth increases at a pretty constant ratio as de- 

 scent towards its centre is made in mines. But in par- 

 ticular they appealed to the phenomena of volcanoes. 



The evidence from this source was gathered and 

 elaborated by Mr. G. Poulett Scrope, secretary of the 

 Geological Society of England, who, in 1823, published 

 a classical work on volcanoes in which he claimed that 

 volcanic mountains, including some of the highest- 

 known peaks, are merely accumulated masses of lava 

 belched forth from a crevice in the earth's crust. 



"Supposing the globe to have had any irregular 

 shape when detached from the sun," said Scrope, " the 

 vaporization of its surface, and, of course, of its pro- 

 jecting angles, together with its rotatory motion on its 

 axis and the liquefaction of its outer envelope, would 

 necessarily occasion its actual figure of an oblate 

 spheroid. As the process of expansion proceeded in 

 depth, the original granitic beds were first partially 

 disaggregated, next disintegrated, and more or less 

 liquefied, the crystals being merged in the elastic vehicle 

 produced by the vaporization of the water contained 

 between the laminae. 



" Where this fluid was produced in abundance by 

 great dilatation that is, in the outer and highly dis- 

 integrated strata, the superior specific gravity of the 

 crystals forced it to ooze upward, and thus a great quan- 

 tity of aqueous vapor was produced on the surface of 



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