5oS CALIFOENIAN MOUNTIAN SYSTEM. Book III. 
its length by a space, which is enclosed by a partly con- 
nected partly interrupted system of mountains in the east, 
and by a similar one in the west. 
The greater part of the surface of this space has an ele- 
vation above the level of the sea, which bears the character 
of a table-land, — that is, the two mountain systems form 
the eastern and western border of it, separate it from an 
eastern and western lateral terrace, and. single unconnected 
chains and groups rise scattered upon the inner space itself. 
It is these latter which may confuse the geographer with 
respect to the main character of the orographic structure of 
this part of the world, since they form what may seem to be 
links of connexion between the western and eastern border 
mountains. In California and Oregon, Utah and New 
Mexico, and in the countries farther north, the two 
border-chains are marked pretty distinctly by nature. We 
have here the Eocky Mountains to the east, the Sierra 
Nevada, the Cascade Mountains, and their more northern 
continuations to the west. In Mexico the western border 
consists of the Sierra Madre, and is likewise remarkably 
defined by nature, but the eastern one is greatly broken, 
and consists of that line of detached and irregular groups 
and mountain ranges, which the Rio Grande crosses in the 
defiles and falls of San Carlos. Here the great connexion 
of the component parts can easily be missed. Nevertheless 
I repeat, that if the Eocky Mountains have a southern 
equivalent, it must be looked for in the mountains of West 
Texas, Cohahuila, Nuevo Leon, San Luis Potosi, and 
Vera Cruz ; and if the Sierra Madre has a northern equiva- 
lent, this must be found in the Sierra Nevada, the Cascade 
Mountains, and its northern continuations : because the first 
line forms the eastern, the second the western border of 
the large inner longitudinal basin of the western half of the 
continent. 
