66 CENOZOIC MAMMAL HOKIZONS 



Conditions of deposition. — The volcanic materials of the John Day 

 were chiefly wind blown, as described by Merriam;^ there is little 

 evidence of fluviatile conditions. The Mollusca are terrestrial or air 

 breathing, with the exception of one locality which contains fluviatile 

 Mollusca. The Testudinata, genus Stylemys, are of the Testudo, or 

 terrestrial type; no fluviatile types have been recorded. The so- 

 called beavers (Castoridse) are not the true river-living beavers 

 (Peterson). 



Fauna.^ — The known fauna of the John Day formation as a whole 

 is chiefly of open-forest and savanna-living type. We note the entire 

 disappearance of the ancient fauna, Creodonta-Hysenodontidse, and do 

 not observe the introduction or invasion from Eurasia of any new 

 families of mammals. The major part of the John Day fauna is of 

 upper Oligocene age, but in its latest phases it is perhaps transitional 

 to lower Miocene. The fauna is thus broadly transitional between 

 that of the White River group and the Arikaree formation. 



The more ancient Ischyromyidse having disappeared, the modern 

 Rodentia are represented by 6 existing families — Sciuridae, Castoridae, 

 Geomyidse, Muridse, Leporidse, and Haplodontidse {Allomys, Myla- 

 gaulodon). Among the Carnivora highly varied Canidae abound, the 

 Felidae are numerous but confined to the machaerodont type, and 

 there is a single member of the Mustelidae, Oligohunis. The Peris- 

 sodactyla begin to be reduced to the 3 existing families of Equidae, 

 Tapiridae, and Rhinocerotidae ; the aberrant Chalicotheriidae occur. 

 Among Artiodactyla, the Elotheriidae attain a great size ; in the middle 

 part of the John Day the peccary-like pigs, Dicotylidae, are found in 

 great numbers ; a wider differentiation arises among the Oreodontidae, 

 hut LeptaucJienia does not occur here. In the upper part of the John 

 Day the members of the Camelidae are first recorded (Sinclair) and 

 begin to attain considerable size ; a species of Paratylopus or Miolahis 

 occurs, resembling the species of the lower Arikaree. The lower 

 John Day fauna is so little known that no deductions can be made 

 from it, except that it appears to be closely related to that of the 

 middle John Day. » 



The faunistic comparison of the John Day formation therefore 

 begins with the middle John Day, which is highly fossiliferous and 

 slightly more advanced than that of the upper portion of the Brule 

 clay and ^^Protoceras sandstones," as will now be shown. 



o A contribution to the geology of the John Day basin; Bull. Univ. California, Dept. Geology, vol. 2, 

 1901, pp. 269-314. 

 bSee Appendix,^. 91. 



