FISHES OF TEXAS AND THE RIO GRANDE BASIN. 
59 
All the rivers along the eastern side of the Plains are supplied from springs, 
mostly from the base of the Cretaceous and Tertiary, but in some instances from the 
Triassic. Many of these springs are quite large and in them are found some Ashes. 
The streams running from them, in many cases, entirely disappear in the ground 
during the dry season, while others dry up. except iu places where the water stands in 
holes or deep pools, in some of which fishes, such as catfish, sunfish, cyprinoids, and 
cyprinodonts, are found in abundance. It has been estimated that not less than 
13,000,000 gallons of water flow over the falls of White River daily, yet nearly the 
entire amount sinks into the ground within a few miles below the falls. 
The soils of the Staked Plains have been derived principally from the underlying 
materials of the late Tertiary. In late Tertiary times the region where the Staked 
Plains now are was an inland sea, bounded on the east and south by the Cretaceous 
formation, and on the west by the range of mountains west of the Pecos River. 
During the early part of this Tertiary time there was great erosion of the Cretace- 
ous and Triassic, and this material of sand and clay was deposited in this inland 
Tertiary sea until finally, when it was drained of its waters, there was left a series 
of beds of this Tertiary material varying from 10 to 12 feet on the south to 300 feet 
on the north, composed of sandy clays in alternate beds of stratification, but none of 
them so compact as to be impervious to water. Whenever these strata are exposed 
to atmospheric influences their material readily disintegrates and forms a soil quite 
homogeneous throughout the entire area of the Plains. This soil is composed chiefly 
of sand and clay with considerable alkali, and, being easily eroded, of course materi- 
ally affects the purity of the streams during the rainy season. While there is 
but little woody vegetation on the Llano, the region is by no means a desert — bunch, 
gramma, and mesquit grasses grow with luxuriance and render the Plains valuable 
for grazing. 
The following table gives the temperature at three different places on the Plains : 
Table showing animal mean temperature on the Staked Plains in Texas.* 
Station. 
Eleva- 
tion. 
Jan. 
Feb. 
Mar. 
April. 
May. 
June. 
July. 
Aug. 
Sept. 
Oct. 1 Nov. 
1 
Deo. 
An- 
nual. 
Fort Elliott 
2, 500 
30.6 
36.0 
46.0 
55.6 
63.8 
73.0 
77.0 
74.7 
68.2 
56.8 42.5 
34.4 
54.8 
Mount Blanco . . . 
3, 800 
43.7 
46.3 
54.3 
61.0 
72.6 
76.8 
78.9 
81.0 
73.0 
61.2 50.6 
40.6 
61.7 
Midland 
2, 775 
39.3 
46.9 
52.1 
64.3 
77.5 
80.0 
84.2 
81.1 
73.3 
61.5 1 48.6 
41.7 
62.3 
The annual rainfall is about 20 inches, the greater part of which falls during the 
summer months. The season of greatest drought is during the winter months. 
5. The Trans-Pecos region . — This embraces all that portion of Texas lying between 
the Pecos and the Rio Grande, and has an average width of about 150 miles and an 
average length of over 250 miles ; its area is, therefore, considerably greater than that of 
the State of Maine. The only true mountains in Texas are in this region, the principal 
ranges being the Guadalupe, Limpia, and Quitman mountains. The general elevation 
is 3,000 to 5,000 feet above the sea, but some peaks rise much higher. Guadalupe Peak 
is 9,000 feet and Limpia Peak 8,000 feet. The summits of most of these mountains are 
covered with a good growth of timber, the principal trees represented being three species 
of pine ( Pinus ponderosa , P. flexilis , and P. edulis), some of which grow to good size. 
*For this table and much of what is here given regarding the climate and geography of the 
western part of Texas we are indebted to the various reports of the Texas Geological Survey. 
