74 GEOLOGICAL SURVEY OP TEXA^. 



The stratigrapliic significance of these species is as follow: In the 

 first place all of them are peculiar to this horizon. In the next place 

 the genera have the following distribution: 



From base of Miocene to recent 2 



From Loup Fork to Equus beds, inclusive 1 



Loup Fork only 2 



Equus bed to recent, inclusive 1 



Equus bed only 2 



Peculiar to the Blanco 3 



Total 11 



Thus five genera occur in the Loup Fork, four in the Equus bed and 

 not in the Loup Fork, and three are peculiar, while three genera still 

 exist. This statement indicates the intermediate character of the 

 horizon. 



In first characterizing this fauna, I pointed out the occurrence of the 

 genus Equus in connection with mastodons with molar teeth of the 

 angustidens type as a relation not previously observed on the North 

 American Continent. I had, however, previously shown such a co- 

 existence in the ancient fauna of the valley of Mexico. Three species 

 of horses coexist there apparently with the Mastodon oligobunis, provided 

 the specimens preserved in the Mexican museums really came from the 

 same horizon. While this coexistence is possible, it is at the same time 

 not yet demonstrated by exact observations on the stratigraphic position 

 of the fossils. No such association has been detected in the Equus beds 

 in North America. Should it be proven to have actually existed in 

 Mexico, a possible antiquity somewhat earlier than that of the Equus 

 bed of the north may be indicated for the bed at Tequixquiac. 



