6(j SURFACE GEOLOGY. 



or of existing glaciers. And here, also, the lofty summits have not been truncated 

 by glaciers or drift agency. 



In America the evidence of ancient glaciers is less striking. I think, how- 

 ever, that I have discovered them upon some of our mountains, and the subject is 

 of such importance, that I have devoted a separate paper accompanying this, to 

 the details of my observations relative to them. 



38. Countries corresponding in their modified drift, or rather their beaches and 

 terraces, may be regarded as having occupied about the same length of time in 

 their last emergence from the ocean, and consequently are of nearly the same sub- 

 aerial age. Perhaps I ought to add, that this principle would require that there 

 should be a general correspondence, also, in the outlines of the surface, and the 

 nature of the rocks, as well as in the rapidity with which the waters withdrew. 

 For, since in my view the terraces and beaches were produced by the drainage of 

 the country, the length of time occupied would depend very much upon the contour 

 of the surface, and the character of the rocks. All these circumstances being the 

 same, I do not see why the time occupied by the drainage should not be the same. 

 In the northern parts of the United States, in Scotland, and Scandinavia, so far as 

 my observation in the two first countries, and information concerning the third, 

 extend, all the above circumstances are essentially alike, and hence I should 

 regard their postdiluvial ages as nearly equal. The facts mentioned elsewhere as 

 to the terraces of the river Jordan, would lead to the conclusion that Palestine 

 and Syria, regarded by so many writers as having experienced great vertical move- 

 ments, have remained essentially unchanged nearly as long as New England ; and 

 the facts respecting the Arabah and its Wadys, south of the Dead Sea, confirm 

 this opinion. This point I have discussed more fully in the first volume of the 

 Transactions of the American Association of Geologists and Naturalists. 



39. It is a well known question of great interest, whether the drainage of con- 

 tinents, since the drift period, has been effected by the elevation of the land, or 

 the depression of the oceans. The able expositions of the latter hypothesis, by 

 Professor James D. Dana, in the American Journal of Science, incline me to adopt 

 it, at least partially, some of the facts, concerning beaches and terraces, affording 

 a presumption in its favor. It is not very easy to conceive how a broad conti- 

 nent can be lifted up, and permanently sustained, to the average height of nearly 

 a thousand feet. Still more difficult is it to imagine how this can be done so as 

 not to rupture or disturb the superficial deposits upon it. We should expect that 

 in some places the elevation would be much greater than in others, and conse- 

 quently the lines of level of the beaches and terraces would be changed, and the 

 materials in some places be disturbed, as they are in regions subject to earth- 

 quakes. But I have never met with a single example of such disturbance. And 

 the only case I know of, is the one described by Mr. Chambers, in Finmark, where 

 a seesaw movement, of more than two feet in a mile, has been traced over an extent 

 of 40 miles. Such cases may be discovered in our country ; but, so far as I can 

 judge, the change of level has been effected here in the most quiet manner, and 

 the surface has risen in every part alike, and its whole contour remains as when 



