GEOLOGIC DISTRIBUTION 



In the following pages, the Duchesne River horizon is considered as partly upper Eocene and 

 partly lower Oligocene, bridging the gap between the top of the Uinta and the base of the Chadron. 

 This position is based on lithological as well as faunal grounds. 



The lower Oligocene Cypress Hills and the Chadron horizons are believed to be equivalent. 

 The Cypress Hills is not to be confused with the older Swift Current horizon. Possibly the latter 

 is equivalent to part of the Duchesne River, and the Pipestone may prove to be the same age as the 

 upper Duchesne River. The fauna of the Pipestone appears somewhat older than that of the 

 Chadron. 



The John Day, I believe, extends from the upper Oligocene into the lower Miocene, the lower 

 and middle divisions belonging in the former, and the upper, in the latter. This supposition seems 

 to be warranted by the time interval involved and by the character of the fauna in the middle and 

 upper divisions. There is a profusion of eporeodonts in the middle John Day and an abundance of 

 promerycochcerids in the upper division, the overlap being about 14 per cent in both groups. It 

 seems to me that the faunal facies is allied with the Great Plains upper Oligocene on the one hand 

 and with the lower Miocene on the other. 



Bed F of Hayden is placed in the upper Miocene, although it may be lower Pliocene, at least in 

 part. 



The Deep River, sensu striclo, is considered here to lie in the lower part of the upper Miocene. 

 Scott (1891C) and Simpson (1933) state that all of Cope's material from the Smith River Valley of 

 Montana was collected in the upper part of the Deep River horizon. The lower part of the old 

 Deep River now is termed Fort Logan and is of lower Miocene age. 



In the upper Oligocene I include the upper Brule, middle John Day, lower Martin Canyon, 

 and Toston beds as very nearly equivalent. The Sespe consists of two distinct parts, as shown by its 

 fauns. The lower portion apparently is near Duchesne River age, while the upper seems to me 

 partly upper Oligocene and partly lower Miocene. 



The upper John Day, Gering, Monroe Creek, lower Harrison, lower Rosebud, Tecuya, and 

 uppermost Sespe are placed in the lower Miocene. The Gering and Monroe Creek are older than 

 the Harrison beds. There is a decided break between the Harrison and the underlying Monroe 

 Creek. Upper Harrison and upper Rosebud are nearer the top of the lower Miocene than are the 

 preceding horizons. 



Apparently the middle Miocene is poorly represented in the merycoidodont family, the only 

 horizons being the Brown's Park, Cuyama, Sheep Creek, and Bed D of Hayden. 



In the upper Miocene we find many horizons yielding representatives of these animals. The 

 lower Snake Creek, Mascall, Pawnee, Virgin Valley, Deep River, Bed F of Hayden, and probably 

 the Skull Spring horizon seem closely equivalent in faunas and in age. I believe the Flint Creek is 

 also of this age. The Madison Valley and Barstow are considered to be near the top of the upper 

 Miocene. The Mint Canyon probably extends well into the lower Pliocene, but the merycoidodont 

 recorded from that horizon is of an upper Miocene facies. 



The horizons here placed in the lower Pliocene are subject to revision. Stirton, for example, 

 believes the Valentine is transitional from lower to middle Pliocene age. 



In the following lists the geological horizons and the genera are arranged alphabetically. 



Upper Eocene Upper Eocene — Lower Oligocene 



Swift Current — Protoreodon sp. Duchesne River — Protoreodon sp. 



Uinta A — Protoreodon sp. 



Uinta B — Protoreodon -parvus, P. sp. 



Uinta C — Hyomeryx breviceps, Protoreodon Lower Oligocene 



medius, P. minor, P. paradoxicus, P. pumi- Chadron — Limnenetesplatyceps,L.sp.,Mery- 



lus, P. sp. coidodon affinis, Oreonetes anceps 



