172 The Founders of Geology LECT. 



had also observed, from the well-worn fragments of the 

 former enclosed in the latter, that the interval of time 

 represented by the break between them must have been of 

 considerable duration. 



Having, by this admirable train of observation and 

 deduction, been led to the demonstration of former gigantic 

 disturbances, by which the bed of the sea had been up- 

 heaved and its hardened sediments had been tilted, plicated 

 and fractured, to form the existing dry land, Hutton had 

 next to look round for some probable cause for these pheno- 

 mena. He inferred that the convulsions could only have 

 been produced by some force that acted from below up- 

 ward, but was so combined with the gravity and resistance 

 of the mass to which it was applied, as to create a lateral 

 and oblique thrust that gave rise to the contortions of the 

 strata. He did not pretend to be able to explain the 

 nature and operation of this subterranean force. He 

 believed that it was essentially due to heat, and he con- 

 nected with it the operations of volcanoes, which he re- 

 garded as general over the globe, and as " spiracles to the 

 subterranean furnace in order to prevent the unnecessary 

 elevation of land, and fatal effects of earthquakes." x 



Unlike Werner, Hutton recognized the fundamental 

 importance of the internal high temperature of the globe, 

 of which volcanoes are one of the proofs. He saw that no 

 mere combustion of substances could account for this tem- 

 perature, which arose from causes so far different from 

 ordinary combustion, that it might require no circulation 

 of air and no supply of combustible materials to support 

 it. The nucleus of the globe might accordingly "be a 



1 Theory of the Earth, vol. i. p. 146. 



