MUSEUM OF COMPARATIVE ZOOLOGY. 369 



none which have been formed in very deep waters. If this be so, we 

 shall have to admit that the areas now respectively occupied by our 

 continents, as 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 upheaval 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 geo- 

 logical constitution of our continent is satisfactorily known over the 

 greatest part of its extent, it seems to me to afford the strongest evi- 

 dence 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 regular succession, from the oldest azoic 

 and primordial deposits to the cretaceous formation, without the slightest 

 indication of a great subsequent subsidence, seems to me the most com- 

 plete and direct demonstration of my proposition. Of the western part 

 of the continent I am not prepared to speak with the same confidence. 

 Moreover, the position of the cretaceous and tertiary formations, along 

 the low grounds east of the Alleghany range, is another indication of 

 the permanence of the oeean trough, on the margin of which these more 

 recent beds have been formed. I am well aware that in a compara- 

 tively recent period portions of Canada and the United States, which 

 now stand six or seven hundred feet above the level of the sea, have 

 been under water ; but this has not changed the configuration of the 

 continent, if we admit that the latter is in reality circumscribed by 

 the two hundred fathom curve of depth. 



Geologists have appealed very freely to oceanic currents as ac- 

 counting for the presence of loose materials upon the surface of the 

 earth. But now that the actual mode, of distribution of such loose ma- 

 terials, under the action of extensive and powerful currents, begins to be 

 known, those who explain the facts in this way are bound to show that 

 their arrangement actually agrees with the effects of oceanic currents. 

 J must confess that I have looked in vain, in the trough of the Gulf 

 Stream, for traces of the characteristic mud which pours from the 

 mouth of the Amazons in quantities sufficient to discolor the waters 



of the ocean for a great distance from shore; and yet the equatorial 



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