GEOLOGIC HORIZONS AND LIFE ZONES. 



27 



Upper Pawnee Creek, Northeastern Colorado, Matthew, 1913. 



The species of horses of the Upper Pawnee Creek beds (see p. 19), Sand Canon, as observed by Matthew are to be 

 compared with those of the Procamelus-Hipparion zone, both in the milk and permanent teeth. They appear to possess 

 the full generic characters of Protohippus and Hipparion. 



Type of Protohippus proplacidus Osborn, 1918. 



Esmeralda, Nevada, Turner, Merriam, 191G. 



From this horizon camels (Procamelus, Pliauchenia) are abundant, Merycodus furcatus occurs, horses are rare (Mery- 

 chippus, Hypohippus fosborni). 



The Mina locality, a station originally known as the Cedar Mountain beds, contains an exposure which is evidently 

 an extension of the Esmeralda formation (Merriam, letter Sept. 15, 1917). 



The Cedar Mountain sediments are correlated in age with the Esmeralda of the Silver Peak region (Turner), also with 

 the Truckee beds of King (Merriam, 1916, p. 167). 



Ellensburg, Washington, Merriam, 1915. 



" It seems that the Ellensburg formation may be pf considerably later date than the beds containing the typical Mas- 

 call fauna of eastern Oregon." (Merriam, 1915). "It apparently equals the Mascall below and a later horizon contain- 

 ing Hipparion in upper part of the section." (Merriam, 1916). This horizon yields: 



Type of Hipparion condoni Merriam, 1915.5. 



Note: The 77. condoni occurs in a zone in the upper part of the section, several hundred feet above the Mascall flora 

 (Merriam, 1916). 



Madison Valley, Montana, Douglass, 1899. 



Described by Douglass as twenty miles south from the Three Forks of the west side of the Missouri River, perpendicu- 

 lar cliff's composed of clays, fine sands, volcanic ash, and conglomerate, containing referred specimens of Protohippus, 

 Hipparion, Merychippus, Procamelus, Cosoryx, etc. The type of Parahippus (Anchitherium) minimus is attributed to 

 the Madison Valley beds in all of Douglass's references to this species. 



Type of IParahippus (Anchitherium) minimus Douglass, 1S99. 



Flint Creek, Montana, Douglass, 1903. 



Bluffs 100-120 feet in thickness in the valley of the Flint Creek, Montana. Explored by Douglass in 1899. Contain 

 referred Protohippus and Procamelus. The age of these beds is not fully determined. 



Peraceras-Pliauchehia Zone, Lower Pliocene. Pontian, Eppelsheim, Pikermi, in Part. 



The Republican River beds, along the river of the same name in northwestern Kansas, contain very advanced forms 

 of rhinoceros (Peraceras) and of mastodon (Tetrabelodon cam pester). They constitute the type formation of the Peraceras 

 zone of Osborn. 



1. Republican River, upper "Loup Fork," northwestern Kansas, Cope. 



2. Ogallala formation (typical), southwestern Nebraska, Darton, 1899. 



3. Alachua Clays, Archer beds, Florida, Dall, 1892. 



4. Snake Creek beds (in part), western Nebraska, Matthew, Cook, 1909. 



5. Petaluma, California, ?lower Ricardo, Cal., Merriam. 



6. ?Devil's Gulch (upper beds), Niobrara River, Nebr., Barbour. 



