608 HISTORY OF GEOLOGY. 



results of definite causes is concerned. But the 

 various hypotheses which have been propounded on 

 this subject can hardly be considered as sufficiently 

 matured for such calculation. A mass of matter in 

 a state of igneous fusion, extending to the center 

 of the earth, even if we make such an hypothesis, 

 requires some additional cause to produce eruption. 

 The supposition that this fire may be produced by 

 intense chemical action between combining ele- 

 ments, requires further, not only some agency to 

 bring together such elements, but some reason why 

 they should be originally separate. And if any 

 other causes have been suggested, as electricity or 

 magnetism, this has been done so vaguely as to 

 elude all possibility of rigorous deduction from the 

 hypothesis. The doctrine of a central heat, how- 

 ever, has occupied so considerable a place in theo- 

 retical geology, that it ought undoubtedly to form 

 an article in geological dynamics. 



Sect. 4. The Doctrine of Central Heat. 



THE early geological theorists who, like Leibnitz 

 and Buffon, assumed that the earth was orignally a 

 mass in a state of igneous fusion, naturally went on 

 to deduce from this hypothesis, that the crust con- 

 solidated and cooled before the interior, and that 

 there might still remain a central heat, capable of 

 producing many important effects. But it is in 

 more recent times that we have measures of such 



