SOLUTION OF THE WORLD-PROBLEMS. 333 



Freiberg, thought that all the rocks were formed in 

 water, while Yoigt and Hutton (1788) rightly contended 

 that only the stratified, fossil-bearing rocks had had 

 an aquatic origin, and that the Vulcanic or Plutonic 

 mountain ranges had been formed by the cooling 

 down of molten matter. 



The heated conflict of these "Neptunian" and 

 " Plutonic " schools was still going on during the first 

 three decades of the present century ; it was only 

 settled when Karl Hoff (1822) established the principle 

 of " actualism," and Sir Charles Lyell applied it with 

 signal success to the entire natural evolution of the 

 earth. The Principles of Geology of Lyell (1830) 

 secured the full recognition of the supremely important 

 theory of continuity in the formation of the earth's 

 crust, as opposed to the catastrophic theory of Cuvier. 1 

 Palaeontology, which had been founded by Cuvier' s 

 work on fossil bones (1812), was of the greatest 

 service to geology ; by the middle of the present 

 century it had advanced so far that the chief periods 

 in the history of the earth and its inhabitants could 

 be established. The comparatively thin crust of the 

 earth was now recognized with certainty to be the 

 hard surface formed by the cooling of an incandescent 

 fluid planet, which still continues its slow, unbroken 

 course of refrigeration and condensation. The crump- 

 ling of the stiffened crust, n the reaction of the molten 

 fiery contents on the cool surface," and especially the 

 unceasing geological action of water, are the natural 

 causes which are daily at work in the secular forma- 

 tion of the crust of the earth and its mountains. 



To the brilliant progress of modern geology we owe 



1 Cf. The Natural History of Creation, chaps, iii., vi., xv., and xvi. 



