Mr J. D. Dana on the Origin of Continents, 239 



tive altitude to the thickness of the cracked varnish on a 

 twelve inch globe. 



We remark, again, that we exclude none of those causes 

 of elevation usually recognised, which facts shew to have 

 been in operation, though allowing them only a subordinate 

 place. 



From these explanations we proceed to the application of 

 them. 



If the reft.der will place before him a good map of North 

 America, he will perceive at once the effects which have been 

 alluded to exhibited on a grand scale, on both sides of the 

 continent. On the 4tlantic side, the Appalachians, from 

 Maine to Georgia, consist of rock strata, which have been 

 variously folded up into ridges, as has been made out with 

 great beauty and fulness by Professors W. B. and H. D. 

 Rogers.* These folds are in several series, but are nearly 

 uniform or parallel in position. As should be expected from 

 the nature of the cause, the plications are more frequent and 

 abrupt on the side of the chain nearest the ocean, and gra- 

 dually die out westward just beyond the limits of the Appa- 

 lachians. As another result of proximity to the contracting 

 area, the rocks on the eastern side have been most altered 

 by fire. To so great a degree has the heat operated, (which 

 escaped by the opened cavities and fissures, and was distri- 

 buted laterally by the aid of the contained and incumbent 

 waters,) that it is difficult in New England to distinguish the 

 true igneous rocks from those that are metamorphic. 



On the Pacific side of the continent, we observe the Rocky 

 Mountain range rising with a gentle swell from the coast. 

 From the mouth of the Kansas to the top, and on the opposite 

 or western side, the average slope is hardly twelve feet to 

 the mile.t The summit is about eight thousand feet high. 



* Trans, of the Assoc, of Amer. Geol. and Nat., 1840, 1842, p. 474, and 

 Amer. Jour, of Science, xliii., 177 j xliv., 359. 



t See the section of the region between the mouth of the Kansas and Fort 

 Vancouver, by Captain Fremont, in the Report of the Exploring Expedition to 

 the Hooky Mountains in 1842, and to Oregon and North California in 1843, 

 1844. Printed by order of the Senate of the United States, Washington, 1845. 



