Ii8 RE. Clements 



prevailing in this region in Ricardo time were probably not widely 

 different from those now obtaining in the southern portion of the 

 Great Valley of California. 

 The same authority states that the mammals of Thousand 



Creek suggest plains with meadows or occasional lakes; the 

 rainfall may have been somewhat higher and the temperature 

 rather lower than at present (1911:219). Merriam, Stock, and 

 Moody (1925:59) make no statement concerning the vegetation 

 and climate of the Ratdesnake formation, but the comparison 

 with the Ricardo and Thousand Creeek clearly indicates that 

 these three must have been much the same throughout, the more 

 advanced character of the Rattlesnake being offset by the south- 

 ern position of the Ricardo. 



In support of the assumption of a widespread prairie climax 

 during the Pliocene may be adduced the occurrence of the major 

 grazing genera in the Middle West. Three species of Hipparion 

 are recorded for the Snake Creeek of northwestern Nebraska, 

 two for Florida, and one for the Blanco of Texas. The Blanco 

 also exhibits one species of Pliohippus; the Clarendon of the 

 same state, two species; the Snake Creek, three; and South Da- 

 kota horizons, two. The Snake Creek and neighboring Valen- 

 tine contain two species of Procamelus, and the former has one 

 species of Pliauchenia. Of Merycodus, the Snake Creek has one 

 form, the Valentine two, and the Santa Fe of New Mexico two. 



