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 Andes, 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 Andup, Rov ; ‘hawe:sieen: to; that i 
while the coast of New Ei d th states has been 
elevated only a few hapteed: fonts mS the southern st states aa - 
lift appears to have been still less. * | 
The Appalachian range of mountains pepe a ousiak 
tidge, extending northeasterly through New England, and not 
improbably to Labrador. The rise of this chain elevated the 
eretaceous 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 asynclinal 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 ensemnele the Connecticut 
Vol. xx1, No. 2.—July-Sept. 1841. 
