136 THE HISTORY OF SCIENCE 



that the denudation ever in progress would be event- 

 ually fatal to the sustenance of plant and animal and 

 man, if the earth were not a renewable organism, in 

 which repair is correlative with waste. 



All strata are sedimentary, consolidated at the 

 bottom of the sea by the pressure of the water and 

 by subterranean heat. How are strata raised from 

 the ocean bed ? By the same subterranean force that 

 helped consolidate them. The power of heat for the 

 expansion of bodies, is, says Hutton (possibly hav- 

 ing in mind the steam engine), so far as we know, 

 unlimited. We see liquid stone pouring from the 

 crater of a lofty volcano and casting huge rocks into 

 mid-air, and yet find it difficult to believe that Vesu- 

 vius and Etna themselves have been formed by vol- 

 canic action. The interior of the planet may be a 

 fluid mass, melted, but unchanged by the action of 

 heat. The volcanoes are spiracles or safety-valves, 

 and are widely distributed on the surface of the 

 earth. 



Hutton believed that basalt, and the whinstones 

 generally, are of igneous origin. Moreover, he put 

 granite in the same category, and believed it had 

 been injected, as also metalliferous veins, in liquid 

 state into the stratified rocks. If his supposition 

 were correct, then granite would be found sending 

 out veins from its large masses to pierce the strati- 

 fied rocks and to crop out where stratum meets stra- 

 tum. His conjecture was corroborated at Glen Tilt 

 (and in the island of Arran). Hutton was so elated 

 at the verification of his view that the Scotch guides 

 thought he had struck gold, or silver at the very 

 least. In the bed of the river Tilt he could see at 



