THE STORY OF NINETEENTH-CENTURY SCIENCE 



posing schools ; though it should not be forgotten that, 

 meantime, the members of the Geological Society of 

 London were making an effort to hunt for facts and 

 avoid compromising theories. Fact and theory, how- 

 ever, were too closely linked to be thus divorced. 



The brunt of the controversy settled about the un- 

 stratified rocks granites and their allies which the 

 Plutonists claimed as of igneous origin. This contention 

 had the theoretical support of the nebular hypothesis, 

 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 in- 

 creases at a pretty constant ratio as descent towards its 

 centre is made in mines. But in particular they ap- 

 pealed 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. The 

 Neptunists stoutly contended for the aqueous origin of 

 volcanic as of other mountains. 



But the facts were with Scrope, and as time went on it 

 came to be admitted that not merely volcanoes, but many 

 " trap " formations not taking the form of craters had 

 been made by the obtrusion of molten rock through fis- 

 sures in overlying strata. Such, for example, to cite 

 familiar illustrations, are Mount Holyoke, in Massachu- 

 setts, and the well-known formation of the Palisades 

 along the Hudson. 



But to admit the "Plutonic" origin of such wide- 



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