THE CONTINENTAL ICE-SHEET 



basins by unequal radial contraction, that the sub-ocean 

 crust would be denser in proportion as it has contracted 

 more and the radii shorter, and the continental masses 

 lighter in proportion as they have contracted less, and 

 their radii longer; therefore, also, the continental masses 

 and the sub-oceanic material are in isostatic equilibrium. 

 This idea was originated later by Button, but is a neces- 

 sary result of Dana's views. 



The Continental Ice-Sheet 



I have dwelt on this idea of the development of the 

 earth as a unit because it is the grandest and most origi- 

 nal of Dana's ideas, and that on which his claims to 

 greatness must mainly rest ; but there are also other ideas 

 which, if they did not originate with him, were worked 

 out by him with untiring energy and consummate skill. 

 The most important among these, perhaps, is that of the 

 continental ice-sheet. 



We have already spoken of the effect of Agassiz's 

 development-views on Dana. The fact is, there was 

 much in common in the character of the minds of the two 

 men. Both were in a marked degree men of advanced 

 thought and spirit. If Agassiz had the advantage of in- 

 tenser enthusiasm and perhaps greater genius, Dana had 

 the advantage of wider knowledge of science in many de- 

 partments and more systematic and orderly methods of 

 work. When Agassiz first brought out his views of the 

 ice-sheet origin of the drift, nearly all geologists, and 

 indeed scientific men generally, regarded them as in the 

 last degree chimerical. Humboldt wrote immediately 

 entreating him as he valued his reputation to reconsider 

 his extravagant views. Dana, on the contrary, at once 

 embraced them with ardor. Now that the contest has 

 ceased and Agassiz's views, pruned of some of their ex- 

 travagant features, have triumphed, on looking back over 

 the ground the important part that Dana played in this 



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