356 THE AGE OF MAMMAI^S 



ccne times in North America. These animals must have swarmed in great 

 herds over the prairies, the conservative or browsing types dwelUng in the 

 woodlands and copses. A marked approximation to the dental t3T:)e of 

 Eqiius is seen in certain varieties of Neohipparion found in this deposit, 

 while certain varieties of Pliohippus approximate the South American 

 Pleistocene horse Hippidion. There is no conclusive evidence that any 

 of these horses were monodactyl, nor among the thousands of teeth pre- 

 served can a single one be referred to the genus Equus. 



Among the camels the typical camel of the Upper Miocene (Procamelus) 

 is well represented, as well as the giraffe camel {Alticamelus) . Mingled with 

 them are remains of gigantic pliauchenias, equaling in size and robustness 

 those of the Middle Pliocene (Blanco Formation). The peccaries belong 

 to the Upper Miocene genus Prosthennops, although the teeth begin to 

 approach those of the Lower Pleistocene Platygonus. The remains of the 

 American Cervicornia and of the merycodonts also present a mixture of 

 Upper Miocene and of more recent character. 



The rodents are again represented by the mylagaulids, or horned go- 

 phers, by the pocket gophers and primitive beavers. Among the latter we 

 find Dipoides, an animal also observed in the Pliocene of China (Schlosser) 

 and regarded by Matthew as possibly related to the Castoroides of the 

 Pleistocene. 



Among the carnivores are lions and saber-tooth tigers, amphicyons and 

 cyons, selurodons and true wolves (Tephrocyon), cacomistles (Bassariscus) , 

 and mustelids of several genera. (W. D. Matthew.) 



Virgin Valley and Thousand Creek of Nevada 



Reference has been made above (p. 338) to the astonishing discovery of 

 strepsicerine antelopes or kudus in northwestern Nevada.^ The sequence 

 of the Tertiary formations in this region is as follows : 



Terrace formations Quaternary, late 

 Epoch of canon-cutting (and of extensive faulting) Quaternary, early 



Deposition of Mesa Dolorite Quaternary to Pliocene 



Thousand Creek section Pliocene to late Miocene 



Virgin Valley Formation Pliocene to early Miocene 



Epoch of erosion and faulting Miocene 



Puebla Range series ( = ?Columbia Lava) Miocene to Oligocene 



The Virgin Valley Formation proper as explored by Merriam probably 

 exceeds 1,500 feet in thickness; it is composed chiefly of volcanic ash and 

 tuffs, the included gravels, sands, clays, lignitic and diatomaceous deposits 

 being of much smaller volume than those of purely volcanic origin. 



' Merriam, J. C, The Occurrence of Strepsicerine Antelopes in the Tertiary of North- 

 western Nevada. Univ. Cal. Publ., Bull. Dept. Geol., Vol. V, no. 22, pp. 319-330. 



