CONTINENTS AND OCEANS. 673 



circumscribed by the two hundred fathom 

 curve or thereabout, and the oceans at greater 

 depth, have from the beginning retained their 

 relative outline and position ; the continents 

 having at all times been areas of gradual up- 

 heaval with comparatively slight oscillations 

 of rise and subsidence, and the oceans at all 

 times areas of gradual depression with equally 

 slight oscillations. Now that the geological 

 constitution of our continent is satisfactorily 

 known over the greatest part of its extent, it 

 seems to me to afford the strongest evidence 

 that this has been the case ; while there is no 

 support whatever for the assumption that any 

 part of it has sunk again to any very great 

 depth after its rise above the surface of the 

 ocean. The fact that upon the American 

 continent, east of the Rocky Mountains, the 

 geological formations crop out in their regu- 

 lar succession, from the oldest azoic and pri- 

 mordial deposits to the cretaceous formation, 

 without the slightest indication of a great sub- 

 sequent subsidence, seems to me the most 

 complete and direct demonstration of my prop- 

 osition. Of the western part of the conti- 

 nent I am not prepared to speak with the 

 same confidence. Moreover, the position of 

 the cretaceous and tertiary formations along 



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