6 ON THE ZOOLOGICAL POSITIOX OF TEXAS. 



and continues southward and westward, passing close to Austin, the 

 State capital, and within twenty miles of the city of San Antonio, ex- 

 tending westward to the valley of the Eio Grande. The portion of the 

 limestone thus elevated is said to be older than that which occupies 

 the adjoining loAvlands, being correlated by some geologists with the 

 ]^o. 2 of Meek and Hayden, while the lower part of the formation is 

 said to represent their No. 3. Without criticizing these determinations, 

 it may be observed that the fault which should exist, if this identifica- 

 tion be true, has been observed at various points along the line of ele- 

 vation. I found it crossing the Helotes Creek eighteen miles from San 

 Antonio at a locality pointed out to me by Mr. Gabriel W. Marnock. 



This steppe of elevation is from five to eight hundred, and occasion- 

 ally a thousand feet in height. Its summit is a greatly interrupted plain, 

 which extends northward to near the Concho Eiver, having a width of 

 nearly two degrees of latitude. Here another elevation takes place, 

 followed by a plain which extends away to the next ascent, which forms 

 the southern boundary of the Staked Plains. The eastern and southern 

 border of this plateau is 3,000 feet above the sea level,* and an ascent 

 of another thousand feet is accomplished before the eastern boundary of 

 New Mexico is reached. 



The rivers of Texas, from the Trinity westward, take their rise at or 

 near the first, second, and third lines of elevation above mentioned. 

 Much the greater number of important streams originate in the region 

 between the first and second steppes of a thousand feet each. This 

 plateau is therefore cut up by their courses, and by the extensive lateral 

 drainage belonging to each, so as to constitute a most varied and inter- 

 esting country. The creeks and rivers flow through canyons or wide 

 valleys with precipitous sides; and the upland is divided into mesas or 

 plains as the canyons are more or less numerous and widely excavated. 

 Near the southern and eastern border the erosion has been so extensive 

 as to leave ranges of rounded hills to mark the former extent of the high 

 land. This hill and canyon region abounds in fine scenery, and is the 

 most picturesque section of the State, excepting the mountains of the 

 Pecos, and the Guadalupe range. 



Climatically considered, Texas embraces two distinct areas. The por- 

 tion which lies east of the ninety-seventh meridian, including one-third 

 of the State, receives the rains which the southern winds bring as clouds 



* Sec list of elevations iu United States, priucipally west of Mississippi Elver, by 

 Henry Gannett, U. S. Geol. Survey Terrs., 1877. 



