1856.] Physical Geography of North America. 173 



on a stupendous scale, and many of their summits are sharply 

 notched and serrated like the Alps. The main eastern range rises 

 like a huge rampart above the great table land at its base, present- 

 ing a deeply gashed flank and vast mountain buttresses towards the 

 plain. Longitudinally the whole chain consists of many sections 

 broken by deep passes, and by the cessation of the leading ridges, 

 which, in many instances, do not join, but lap past each other. 

 This recently ascertained feature presents unexpected facilities for 

 the construction of railways, and other avenues of communication 

 across the continent. In Northern Mexico the eastern range is the 

 Cordillera of Cohahuela and Potozi, the Guadaloupe Mountains 

 being only an outlying chain of ridges ; and the western range is 

 the Sierra de los Mimbres. Opposite the sources of the Arkansas, 

 the eastern belt is the Moro and Chowatche, or Wet Mountain ; 

 and the western the San Juan, and La Plata Mountains. The 

 noble valley of the Rio del Norte is here embraced between the 

 two ranges. From the Arkansas to the north fork of the Platte, 

 the chain is more complex and triple ; its eastern range, comprising 

 the Medicine Mountains, contains some of the loftiest peaks of the 

 Rocky Mountains : such are the Spanish Peaks, Pike's, Long's, and 

 Laramie's Peaks, all rising to 10,000 and 12,000 feet above the sea. 

 North of the Platte rise the Wind River Mountains, the loftiest 

 division of the chain. Here Fremont's Peak has an elevation of 

 13,.568 feet. This high mountain axis is the focal watershed of 

 the continent, for it parts the head fountains of the Missouri flowing 

 to the Atlantic, from those of the Columbia and Rio Colorado, 

 descending westward to the Pacific. 



Branching southward from the Rocky Mountains, near the 

 Wind River range, is the long and lofty chain called the Wahsatch. 

 It is the eastern boundary of the Great Utah Desert, and the west- 

 em barrier of the basin of the Rio Colorado, the Rocky Mountains 

 being the eastern. Northward of the Wind River chain. the eastern, 

 or main axis of the Rocky Mountains, is exceedingly high, where it 

 divides the middle and northern streams of the Columbia from the 

 sources of the Missouri and Saskatchawan. Near the head of the- 

 latter great river Mount Hooker towers to the height of 15,700 

 feet above the sea ; and a little further north, Mount Brown, the 

 feeder of the river Athabasca, reaches the yet greater altitude 

 of 15,990 feet. From this culminating district the chain gradually 

 declines northward to the Arctic Ocean. Beyond lat. 6&^ the main 

 eastern crest ceases to be the watershed between the Pacific and 

 Hudson Bay or the Arctic Ocean. 



The geological constitution and structure of the Rocky Moun- 

 tains are very imperfectly known. Granite and gneissic rocks, and 

 various palaeozoic strata, including much carboniferous limestone, 

 have, however, been extensively noticed in many districts. Between 

 the higher ridges occur table lands and valleys, consisting apparently 

 of cretaceous and tertiary deposits. 



