HISTORICAL GEOLOGY 65 



fair published his Illustrations of the Huttonian Theory 

 of the Earth, of which Geikie says, "Of this great classic 

 it is impossible to speak too highly/' as it is at the basis 

 of all modern geology. 



One of Hutton 's fundamental doctrines is that the 

 earth is internally hot and that in the past large masses 

 of molten material, the granites, have been intruded into 

 the crust. It was these igneous views that led to his 

 followers being called the Plutonists. Another of his 

 great doctrines was that "the ruins of an earlier world 

 lie beneath the secondary strata, ' ' and that they are sep- 

 arated by what is now known as unconformity. He 

 clearly recognized a lost interval in the broken relation 

 of the structures, and that the ruins, the detrital mate- 

 rials, of one world after another are superposed in the 

 structure of the earth. 



Hutton also held that the deformation of once horizon- 

 tally deposited strata was probably brought about at dif- 

 ferent periods by great convulsions that shook the very 

 foundations of the earth. After a convulsion, there was 

 a long time of erosion, represented by the unconformity. 

 Geikie says, "The whole of the modern doctrine of 

 earth sculpture is to be found in the Huttonian theory. ' ' 



The Lyellian doctrine of metamorphism had its origin 

 in Hutton, for he showed that invading igneous granite 

 had altered, through its heat and expanding power, the 

 originally water-laid sediments, and that the schists of 

 the Alps had been born of the sea like other strati- 

 fied rocks. 



Hutton is the father of the Uniformitarian principle, 

 for he "started with the grand conception that the past 

 history of our globe must be explained by what can be 

 seen to be happening now, or to have happened only 

 recently. The dominant idea in his philosophy is that 

 the present is the key to the past." This principle has 

 been impressed on all later geologists by Sir Charles 

 Lyell, and is the chief cornerstone of modern geology. 



The principle of uniformitarianism has underlain 

 geologic interpretation since the days of Hutton, Play- 

 fair, and Lyell. However, it is often applied too rigidly 

 in interpretations based upon the present conditions, 

 because in the past there were long times when the topo- 



