8 FOREST BELTS OF WESTERN KANSAS AND NEBRASKA. 
The great sand-hill region, which stretches from the North Platte 
northward to the Niobrara, and covers approximately one-third of 
the State, with its endless succession of hills and ridges, basins and 
valleys, is as monotonous in a way as the level plains of western 
Kansas. Both are seemingly boundless, and the eye may range over 
them for miles without hindrance. (See Pl. II, fig. 1.) 
STREAMS. 
The principal rivers of western Nebraska and western Kansas are 
the Niobrara, North Loup, Middle Loup, South Loup, Dismal, North 
Platte, South Platte, Republican, North Solomon, South Solomon, 
Saline, Smoky Hill, Arkansas, and Cimarron. There are numerous 
tributary creeks and streams. (See map.) None of the rivers nor- 
mally carries a large volume of water, and some of them, as well as 
many of the creeks, go dry durmg periods of deficient rainfall. 
Yet, even when no water is visible in the beds of such streams as the 
Platte and the Arkansas, one has but to dig down in the sand a foot 
or two to find water in abundance. There is a constant underflow, 
and trees growing in the valleys of these streams do not suffer 
because the surface flow occasionally ceases. 
ROCK. 
Outeropping rock is wholly absent over large areas in western 
Kansas and western Nebraska. Most of the rock found is of two 
general classes, sandstone and lmestone, both of which easily disin- 
tegrate and form soil. Pine Ridge in Nebraska is especially char- 
acterized by the soft, Hght-colored Arikaree sandstone. Shale is 
abundant in many places, and, when broken down, produces clay and 
gumbo soils. In western Kansas and southwestern Nebraska there 
are extensive bodies of irregular, coarse-grained, mortarlike rock of 
Tertiary formation, locally known as * mortar beds ” or “ magnesia.” 
The unconsolidated Tertiary deposits often consist of beds of mate- 
rial ranging from sand to coarse gravel, brought down from the 
Rocky Mountains, and showing forms characteristic of such long 
transportation. 
SOIL. 
All the main streams have sandy beds, and for the most part sandy 
loam or loam soils in their valleys. The smaller streams are com- 
monly less sandy, and many of them have fairly heavy soils. Corre- 
lated with this difference in soil is a marked difference in the species 
of trees and their manner of growth. The cottonwood and willow 
are the only native broadleaf trees which really prefer a sandy soil, 
so they often form the sole tree growth along the larger streams. This 
