ON THE ZOOLOGICAL POSITION OF TEXAS. 5 



dry regions to the westward of it. Like the Austroriparian region of 

 Xorth America it abounds in Batracliia^ including salamanders ; turtles 

 also, though less numerous, are well represented; and lizards and 

 snakes abound. The salamanders mostly belong to a genus, Spelcrpes, 

 which has its headquarters in Xorth America, and several genera of 

 Il^orth American snakes and lizards are abundant there, but they are so 

 mixed with forms of the Tierra Caliente that I regard these districts for 

 the present as faunally inseparable. 



Ha^ing fixed approximately at some points the southern boundaries 

 of the Sonoran and Austroriparian regions of the nearctic realm, the 

 mutual relations of these divisions remain to be considered. And in 

 connection with these we must endeavor to fix the southern limit of the 

 Central region also, whose southern extremity is bordered by both of those 

 above mentioned. It is needless to say that the great State of Texas 

 is the field where these boundaries must be sought for; since, though 

 politically one, its fauna is of a most diversified character. 



Geologically, it was shown by Shumard to be divided, like the Eastern 

 States, by northeast and southwest strikes. If a line is drawn through 

 points a little west of the cities of Dallas and Houston, it will corre- 

 spond nearly with the strike of the eastern border of the marine creta- 

 ceous formation, which constitutes so large a part of the surface of 

 Texas. To the eastward of this line a belt of the Laramie formation 

 extends from the northeast and terminates at the south, without con- 

 tinuing immediately to the west, according to Forshey. East of this 

 the formations of the country are altogether tertiary. The marine cre- 

 taceous of Xortheru Texas soon yields on the west to carboniferous beds 

 which rise fi'om beneath them. These again descend, according to the 

 geologists who have reported on the subject, and are followed by an ex- 

 tensive area of overlying rocks of permian and triassic age. But these 

 formations alike disappear to the southward and are replaced by the 

 western extension of the marine cretaceous. This formation covers a 

 great extent of country in Western Texas, reaching from the latitude of 

 San Antonio, far north into the Staked Plains and IsTew Mexico. 



Topographically speaking, Eastern Texas is a plain varied by mounds 

 of red sand of late tertiary age, and by ravines and shallow valleys of 

 erosion. Extensive prairies cover the foundation of Laramie and marine 

 cretaceous throughout the eastern middle line of the State. The first 

 line of elevation is formed by a break in the latter formation. An ab- 

 rupt elevation commences somewhere to the southwest of Fort Worth 



