J. D. Dana on American Geological History. 311 
In the outset we are struck with the comparative simplicity 
of the North American continent, both in form and structure. 
Th outline, it is a triangle, the simplest of siasthenandital figures ; 
in surfiuce, it is only a vast plain lying Sv lice two mountain 
ranges, one on either border, the Appalachian from Labrador to 
; _ Alabama on the east, the Rocky Mountains on eas west; and on 
its contour it has water, east, west, north, and south. 
Observe too that its border heights are proportioned to the 
size of the oceans. A lofty chain borders the one 
_ the narrow gi while the small Arctic ple is ‘fheed by no 
pro ir mountain range. 
— is principle, ‘that the highest mountains of the continents 
face the largest oceans, is of wide ap perce aa ar unlocks many 
mysteries in physical eeography. South ca lies between 
: Am 
pg ~ tinent i is there pinched up almost to a narrow mountain ridge. 
ers from North America in having a large. expanse of 
ocean, the Atlantic, on the north; and, correspondingly, it has its 
og northern mountain ridges. The world is full of such illustra- 
- - Mons, _but I pass them by. 
tions and extent of the oceans, they seeming to point to the con- 
3 clusion, that the cp neat of the oceanic basins had ricci 
| © ie continental fea tures; and that farther, both results were 
= _-Volved i cing the earth’s gradual refrigeration, and consequent “a. 
ex aatinmicn has thus the simplicity of a single evolved result. 
— = on the contrary, is a wor. d of complexities, It is but 
one corner of the Oriental continent,—whic includes Europe, 
i ocean bounds it on the a 
a etiasy. 
wide contrast accounts for the greater completeness or 
-of American revolutions, the more abrupt limits of 
h Rha Combine researches of a large number of investi- 
The names of MACLURE, SILLIMAN, Eaton, lead off the 
