308 University of California Publications in Geology [Vol. 8 



that proboscidean remains are not certainly known in America in 

 horizons earlier than middle Miocene and are unknown in the John 

 Day of Oregon with which the Truckee was originally compared. The 

 bearing of the tooth upon the age of the Truckee beds is that it 

 indicates the date of their deposition as middle or upper Miocene or 

 later. In view of the length of post-Truckee time, as evidenced by the 

 diastrophic, volcanic, and erosional history since the deposition of 

 these beds, it seems probable that the Truckee is not younger than 

 Miocene. It seems not improbable that the Truckee beds are approxi- 

 mately the equivalent of the Esmeralda, determined to be of middle 

 or upper Miocene age on the basis of mammalian remains, although it 

 is possible that the two formations do not represent exactly identical 

 horizons. 



Transmitted October 14, 1914. 



