ON NORTH AMERICAN ZOOLOGY. 123 



son *, and dissent from those who consider the Isthmus of Da- 

 rien as a zoological boundary f. 



Physical Geography. 



The great range of the Rocky Mountains forms a most re- 

 markable feature in the physical aspect of North America. 

 Viewed as a continuation of the Cordilleras de los Andes of the 

 southern continent, and extending from the Straits of Magalhaes 

 to the Arctic sea through 120° of latitude, it is by far the longest 

 mountain chain in the world. In Mexico it divides into three 

 bi'anches ; the western one passing through the province of 

 Guadalaxara to the Rio Gilaj the eastern one extending through 

 the Texas towards the confluence of the Missouri and Missis- 

 sippi, where it terminates after assuming the appellation of the 

 Ozark Mountains ; and the highest or central branch con- 

 tinuing northwards to between the 29th and 30th parallels of 

 latitude, where it is linked to the lateral forks by connecting 

 spurs, or as Humboldt names them '* counter forts." Within 

 this mountain system, between the parallels of 19° and 24^°, lie 

 immense table lands, elevated to the height of 6000 or 7000 

 feet above the sea. The central Cordillera of Mexico has a di- 

 rection of N. 10° W. from the 25th to the 38th degree of latitude ; 

 and from thence the course of the ridge is with very slight de- 

 flections about N. 28° W. to the 69th parallel and 138th meri- 

 dian, near the mouth of the Mackenzie, where the Rocky Moun- 

 tains terminate. Travellers, who have crossed the mountains at 

 various parts, inform us that they are divided into several pa- 

 rallel ridges; this is the case near the sources of the Rio del 

 Norte ; again between the 37th and 41st parallels ; in the 58th 

 parallel ; and lastly, in the 64th, where according to the report 

 of the fur-hunters thirteen successive ridges must be crossed 

 before the western declivity is attained. Many of the peaks of 

 the Rocky Mountains rise to a considerable altitude : thus, 

 Spanish Peak, lat. 37° 20' N. ; James Peak, 38° 38'; and Bighorn, 

 lat. 40°, have been ascertained by officers of the United States 

 to be from 10,000 to 12,000 feet in height. Mount Hooker and 

 Mount Brown, in the 52nd and 53rd parallels, were stated by the 

 late Mr. Douglas, but from less perfect data, to be respectively 

 15,690 and 15,900 feet above the sea. It is manifest that ani- 

 mals may travel along the acclivities of a mountain chain whose 

 summits enter within the limits of perpetual snow, from the 



* Encyclopcedia of Geography, 1834; Geography and Classification ofAni- 

 tiimals, by William Swainson, Esq., 1835, 

 t Penny Cyclop<edia, art. America. 



