Address before the Association of American Geologists. 265 



the latter. But there is another fact that makes this almost cer- 

 tain, or it shows at least, that the western, and particularly the 

 southwestern part of the continent, has been raised to a much 

 greater height than the eastern side. It is well known that the 

 cretaceous formation of North America passes under the Atlantic 

 Ocean near New York, with its superincumbent tertiary strata. 

 The latter reappear on Long Island, and in great distinctness 

 on Martha's Vineyard, near the coast of Massachusetts, beyond 

 which they are no more seen south of Greenland. But as we 

 go southwesterly from New York, the chalk formation gradually 

 rises, and between Council Bluff and the Rocky Mountains, as I 

 am informed by Mr. Nicollet, it sometimes reaches the height of 

 two thousand feet, which is much higher than on the Atlantic 

 coast. It appears, also, from the recent memoir of Von Buch, 

 on the petrifactions of South America, that the same formation 

 exists extensively developed in the Ancles, from 10° north to 15° 

 south latitude. It there attains the astonishing height of thir- 

 teen thousand feet above the ocean. Subsequent to the cretace- 

 ous period, therefore, the Andes must have risen to that height ; 

 while the coast of New England and the middle states has been 

 elevated only a few hundred feet. In the southern states the up- 

 lift appears to have been still less. 



The Appalachian range of mountains forms another anticlinal 

 ridge, extending northeasterly through New England, and not 

 improbably to Labrador. The rise of this chain elevated the 

 cretaceous and tertiary rocks on the Atlantic slope, as well as the 

 new red sandstone, and tilted up the southeastern margin of the 

 transition rocks in the valley of the Mississippi. The uplift of 

 the Rocky Mountains raised the western side of the same rocks, 

 and produced the easterly slope of the strata extending to the 

 Mississippi. That river, therefore, flows through a synclinal val- 

 ley, and it was the existence of that valley which determined its 

 course. The same is true of the river Ohio, which, according to 

 Dr. Hildreth, flows through a synclinal valley. The sections given 

 by Prof. Emmons, show that the same is true of the St. Lawrence. 

 From the last report of Mr. Houghton, it appears that Lake Su- 

 perior occupies a synclinal valley, and not improbably a valley 

 of elevation. East of Little Falls, according to Mr. Conrad, the 

 Mohawk flows many miles through a valley of depression. In 

 New England, the primary strata dip towards the Connecticut 



Vol. xn, No. 2.— July-Sept. 1841. 34 



