MEMOIR OF JAMES D. DANA. 471 



these, and the one that Dana first announced, was the "Appalachian 

 revolution," which occurred at the end of the Paleozoic. Other revolu- 

 tions have been brought out by Dana and by 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 basins by unequal radial contrac- 

 tion, 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 ; there- 

 fore, also, the continental masses and the sub-oceanic material are in 

 isostatic equilibrium. This idea was originated later by Dutton, but is 

 a necessary result of Dana's views. 



I have dwelt on this idea of the development of the earth as a unit 

 because it is the grandest and most original 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 intenser enthusiasm 

 and perhaps greater genius, Dana had the advantage of wider knowledge 

 of science in many departments 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 imme- 

 diately entreating him as he valued his reputation to reconsider his 

 extravagant views. Dana, on the contrar}^ at once embraced them with 

 ardor. Noav that the contest has ceased and Agassiz's views, pruned of 

 some of their extravagant features, have triumphed, on looking back over 

 the ground the important part that Dana played in this controversy is 

 evident. Many others have contributed largely to the establishing of 

 the fact of the existence of a North American ice-sheet and determining 

 its limits, chief among whom must be mentioned Chamberlin, Upham, 

 Hitchcock, Lewis, Wright, and others ; but Dana was their leader, not 

 only in first embracing the idea, but in abundant, painstaking, detail work 

 on the phenomena in New England. 



If time permitted we might take up many other subjects which he 

 touched only to illuminate, subjects which in his mode of handling showed 

 that rare combination of original thought and painstaking, detailed work 

 which characterized him in so remarkable a degree. We can barely 



