88 



CENOZOIC MAMMAL HORIZONS 



Megalonyx, Mylodon; (c) of the Perissodactyla, Equus, 2 species, 

 Tapirus; (d) of the DicotyUdse, Mylohyus. (3) Among newly enter- 

 ing northern forms are: (a) Odocoileus; (b) Ursus, 2 species; (c) 

 Erethizon (the first recorded appearance of the Hystricomorpha in 

 North America). (4) We note the absence of Bovidse. 



Twelvemile Greek, Kansas. — On the plains of western Kansas, in 

 Logan County, on Twelvemile Creek, a tributary of Smoky Hill 

 River, is a deposit formerly considered by Williston^ as of lower 

 Pleistocene age, but now known to be of mid-Pleistocene age. In 

 the blue-gray marl underlying the recent plains marl are recorded 

 ElepJias primigenius {fE. columhi) , Platygonus compressus, and a num- 

 ber of specimens of Bison occidentalis (Lucas). Among Primates, 

 Homo is indicated ^ by the occurrence of an arrowhead certainly 

 associated with the skeleton of Bison occidentalis and believed by 

 Williston to be in situ. 



SUBSEQUENT PHASES OF THE MIDDLE PLEISTOCENE. 



HOMOTAXIS. 



America. — Potter Creek cave, Shasta County, Cal.; Silver Lake, 

 Oregon. 



ENVIRONMENT. 



Environmental conditions on the Pacific coast were quite different 

 from those in the Middle and Eastern States: (1) All glaciation on 

 the Pacific coast was comparatively late in the Pleistocene and of the 

 alpine type (Sinclair). It is quite possible, therefore, that many 

 types of mammals (elephants, mastodons, camels, bisons) survived 

 in the comparatively mild climate of the Pacific coast after they had 

 become extinct in more easterly regions. 



FAUNA. 



Potter Creelc cave. — The very rich Potter Creek cave fauna is 

 regarded by Merriam and Sinclair ^ as a late phase of the middle 

 Pleistocene, or even as late as the last quarter of the Pleistocene. It 

 contains 37 genera and 49 species of mammals, of which 8 genera and 

 22 species are extinct, 3 are doubtfully extinct, and 21 are still exist- 

 ing. It is chiefly a forest fauna; forest types are numerous and 

 plains types are lacking. 



Positively we note the survival or presence of the edentates Mega- 

 lonyx and Nototherium; also of Eguus and ElepJias. Among Artio- 



a Williston, S. W., The Pleistocene of Kansas: Univ. Geol. Survey Kansas, vol. 2, 1897, p. 300. 



b Williston, S. W., On the occurrence of an.arrowhead with bones of an extinct bison: Trans. Intern. 

 Congress of Americanists, 1902, p. 335. 



c Sinclair, W. J., A preliminary account of the exploration of the Potter Creek cave, Shasta County, 

 Cal.: Science, n. s., vol. 17, No. 435, May 1, 1903, pp. 708-712. The exploration of the Potter Creek cave: 

 Univ. California, Publ. Am. Arch, and Eth., vol. 2, No. 1, 1904, pp. 1-27. New Mammalia from the 

 Quaternary caves of California: Bull. Dept. Geology, Univ. California, vol. 4, 1905, pp. 145-161. 



