4 MOUNTAIN SYSTEMS. 
between the headwaters of the streams which flow eastward and those which flow westward. 
It divides the whole area between the Mississippi and the Pacific into two nearly equal 
portions—that on the east being somewhat the larger. This crest of the water-shed has its 
greatest elevation in Mexico; and thence declines to its lowest point about the latitude of 32°, 
where it has a height of about 5,200 feet, between the waters of the Rio Grande and those 
of the San Pedro, a tributary of the Gila. From this parallel it increases in altitude north- 
ward, and reaches its maximum near the 38th parallel, where it is about 10,000 feet high. 
Thence it declines as we pass northward; and, in latitude 42° 24’, it has an elevation of, say, 
7,490 feet; and in the latitude of about 47° it is reported to be at least 1,450 feet lower. The 
heights here given are those of the lowest passes over the crest or water-shed of the great plateau 
of the country, and not those of the mountain peaks and ridges which have their base upon it, 
and rise, in some cases, to the height of 17,000 feet into the region of perpetual snow. : 
The slope of the plateau on the east and south, towards the Mississippi and the Gulf of 
Mexico, is comparatively gentle, and in the northern part of Texas, that known by the name 
of the Llano Estacado, or Staked Plain, is by steps. It is traversed by the Missouri, the 
Platte, the Arkansas, and other large rivers, which rise among the mountains near the crest, 
and flow eastward and southward in channels sunk beneath the general surface-level of the — 
plains. 
Its crest, and nearly the entire distance thence to the Pacific, is occupied by high plains or 
basins, differing from each other in elevation from 1,000 to 3,000 feet, and by mountain peaks 
_ and ridges, varying in direction to almost every point of the compass, though they have a 
general course north and south. Many of these mountains, including those that bound this 
system, have obtained the name of chains, and a short classification of them will now be 
attempted, although it is to be premised that our knowledge of them is most imperfect, and 
the classification now made, future explorations will probably show to be erroneous. The 
only proper classification must be made by the geologist, after a thorough exploration for 
this purpose, which it will require a long period to accomplish. 
These mountains may be considered as constituting three great systems, extending gen- 
erally throughout our possessions in a north and south direction; and though this arrange- 
ment may not be the best or most accurate, yet it will enable us to take a comprehensive 
view of the whole as regards the construction of a railroad, since any direct line that can be 
traced from the Mississippi to the Pacific, except near the 48th and 32d parallels, will 
encounter each of these three systems in some point. 
Calling the most eastern system No. 1, we find a portion of it, crossing the Rio Grande, 
and entering Texas at the Great Cation. Its extension south into Mexico forms the east 
front of the Sierra Madre. Running northward, this system includes all the mountains on 
either side of the Rio Grande, enclosing its valley and the Salinas Basin. Those on the 
east form the divide between the Pecos and Salinas Basin, and between the Rio Grande 
ond Canadian; on the west they divide the waters of the Rio Grande from those that flow to 
the Gulf of California. Those on the east are sometimes called the Rocky mountains, some- 
times the Sierra Madre; and this last name is sometimes applied to those on the west. There 
seems to be a necessity for considering the mountains on both sides of the Rio Grande as one 
system, ‘These may be said to unite near the headwaters of the Rio Grande and Arkansas, 
and here the mountains have their greatest development. The Sierra de la Plata extends 
to the southwest, the Elk mountains to the west, and the various chains forming the Park 
mountains to the north, The Park mountains, in latitude 41° 80/, sink into the plateau, 
forming the region of the South Pass; and the only continuation we have of this system is in 
the Black Hills, which continue to the north, with diminished elevation, till, in latitude 46° 
15', they are merggd into the coteau through which the Upper Missouri makes its passage. 
mong the mountains included in this system are the Sierra Madre, a portion of what is 
called the Rocky mountains, the Diabolo mountains, the Guadalupe mountains, Hueco mount- 
4, 
