LIFE OF JAMES DWIGHT DANA 



without law or goal ; the continents and the oceans had 

 changed many times in the history of the earth. For 

 Dana, on the contrary, earth-forms have steadily de- 

 veloped toward their present condition. The idea of 

 evolution was clearly conceived and applied to the earth 

 (though not to the organic kingdom) by Dana long before 

 Darwin's time. 



Doubtless this idea of permanence of earth-forms may 

 be pressed too far, but was never so pressed by Dana. 

 For him it was not absolute rigid permanence, for that 

 would be contrary to the idea of evolution ; for him it 

 was permanence of thought, of plan, but carried out by 

 development, and therefore with many changes in detail. 

 There have doubtless been many oscillations of the 

 earth's crust, many submergences and emergences of 

 land surfaces, especially on the margins, though some- 

 times of greater extent and affecting also the interior of 

 continents, oscillations the causes of which we do not yet 

 understand ; but with these qualifications and limitations 

 the principle is now well established and generally ac- 

 cepted. 



4. As a necessary consequence of steady contraction 

 resisted by crust rigidity, there must have been paroxysms 

 of yielding and therefore periods of readjustments of the 

 crust to new positions, and therefore also extensive 

 changes of physical geography and corresponding changes 

 in organic forms. These times Dana appropriately called 

 revolutions. They are marked by the formation of great 

 mountain ranges. The greatest of these, and the one 

 that Dana first announced, was the "Appalachian revolu- 

 tion," which occurred at the end of the Paleozoic. Other 

 revolutions have been brought out by Dana and others. 

 The idea has been a most important and fertile one in 

 American geology. 



5. Again, it is almost a necessary corollary from the 

 preceding view of the origin of continents and ocean 



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