422 University of California Publications in Geology [Vol.10 



the John Day Valley and several doubtful species from the imper- 

 fectly understood Idaho beds of Idaho. At that time the Great Plains 

 Pliocene fauna included the Blanco of Texas, and the Republican 

 River doubtfully referred to the same period. The Atlantic fauna 

 consisted of the intermixed Alachua Pliocene and Peace Creek Pleisto- 

 cene, and offered a serious problem in age determination by reason of 

 this mixture. 



Seven years ago description of the Snake Creek fauna, the richest 

 of all American Pliocene mammal assemblages, by Matthew and Cook 1 

 gave the first definite indication of existence of an important Pliocene 

 stage other than that of the Blanco. Immediately following the first 

 study of the Snake Creek came discovery of the interesting Thousand 

 Creek Pliocene fauna 2 of Nevada, with suggestion of similarity to the 

 Nebraska Snake Creek in a number of peculiar types, especially in 

 the presence of antelopes like those of the Old World Pliocene and 

 Miocene. Following the discovery of the Thousand Creek there came 

 to light on the western border of the continent the Ricardo fauna 3 of 

 the Mohave Desert, the Etchegoin, 4 and the Pinole Tuff-Orinda 5 faunas 

 of middle California, while the Rattlesnake fauna of eastern Oregon 

 was increased to dimensions comparable to those of the Thousand 

 Creek, Ricardo, and Blanco. Additional information regarding the 

 composition and age of the interesting fauna of the Idaho formation 

 in southwestern Idaho has also been obtained. 



Through the work of Dr. E. H. Sellards, the Alachua fauna of 

 Florida has received valuable additions, and has had separated from 

 it a considerable number of the elements of more modern aspect, which 

 have heretofore confused interpretation of this assemblage. 



Although at the present time American Pliocene mammal faunas 

 are not as fully known as those of other Tertiary divisions, progress 

 in accumulation and classification of material within the past five 

 years has been relatively more rapid than for any other division of 



i Matthew, W. D., and Cook, H. J., A Pliocene fauna from western Nebraska, 

 Bull. Amer. Mus. Nat. Hist., vol. 26, pp. 361-414, 1909. 



- Merriam. J. C, Tertiary mammal beds of Virgin Valley and Thousand 

 Creek in northwestern Nevada, pt. 2, Vertebrate faunas, Univ. Calif. Publ. Bull. 

 Dept. Geol., vol. 6, pp. 199-304, pis. 32-33, 1911. 



3 Merriam, J. C, Extinct faunas of the Mohave Desert: their significance in 

 a study of the origin and evolution of life in America, Pop. Sci. Monthly, pp. 

 245-264, March, 1915. 



* Merriam, J. C, Tertiary vertebrate faunas of the North Coalinga region of 

 California, Trans. Amer. Philos. Soc, n. s., vol. 22, pt. 3, 44 pp., 1915. 



5 Merriam, J. C, Vertebrate fauna of the Orindan and Siestan beds in middle 

 California, Univ. Calif. Publ. Bull. Dept. Geol., vol. 7, pp. 373-385, 1913. 



e Eighth Ann. Rep. Florida Geol. Surv., pp. 92-100, 1916. 



