70 



CENOZOTC MAMMAL HOETZONS 



MIOCENE. 

 IV. FOURTH FAUNAL PHASE— Continued. 



LOWER MIOCENE (EUROPE, ETAGES AQUITANIEN, BURDIGALIEN). 



13. ARIKAREE FORMATION, PROMERYCOCH(ERUS ZONE (GERING, MONROE 

 CREEK, HARRISON, AND ROSEBUD OF DARTON, HATCHER, AND MATTHEW). 



(Figs. 1, 10, 12-14; PL I.) 

 GENERAL FEATURES. 



Geology and nomenclature. — This Great Plains formation, ofHcially 

 designated Arikaree by the Survey was recognized as horizon D by 

 Hayden, and, as shown in the synonymy below (p. 71), has been vari- 

 ously divided and named by Darton, Hatcher, and Matthew. It is 



Porcupine Butte 

 ^Volcanic ash layer 



Merycochcerus 

 zone 



6/astomeryje 

 Parahippus 



Protomeryx 

 Merycochoerus 

 Merychyus (abundant) 



Calcareous _shaly 

 limestone layers 



JPromery- 



Promerycochcsrus 

 (very abundant 

 cocTioems and charactenstic) 



^^^^ Diceratherium 

 £.Jotheri'um 

 Steneof/ber 

 Hypertragu/us 

 Parahippus (small sp. ) 

 Leptauchenia 



I R U L E ^=r^^^^~^^^=^^^^^^^Leptai2che7xia zone —~ 



Fig. 12.— Columnar section of the Rosebud formation, after observations by Matthew and Thomson, 

 1906. For the chief line of this section see section B, PI. II. 



extensively exposed along the Pine Ridge Bluffs of South Dakota on 

 the south side of White River and along Niobrara River, as mapped 

 by Darton.^ (See PI. I.) It extends more than 100 miles east and 



a Prehminary report on the geology and water resources of the central Great Plains: Prof. Paper 

 U. S. Geol. Survey No.' 32, 1905, pi. 35. 



