264 HENRY F. OSBORN 



tion of native types and of the time of arrival of new types to demarkate 

 our Pleistocene also into great successive life-zones. 



The chief progress made thus far (1909) is that we begin to recog- 

 nize the following divisions of American life : 



Early and mid-Pleistocene life of the plains, Equus Zone; 



Mid-Pleistocene life of the forested regions, Megalonyx Zone ; 



Life of the maximum cold period, Ovihos Zone ; 



Life of post- Glacial times, Zones of Cervus and Homo. 



Especially interesting is the coincidence of the maximum cold 

 period, or Ovibos, Musk Sheep, Zone of America, with the maxi- 

 mum cold period, or Elephas primigenius, Rangijer tarandus Zone of 

 Europe. 



It is obvious that we should never expect to discover as clear 

 demarkation of the life-zones in America as in Europe because of the 

 vast refuge areas of the mammals in the south. In Europe the 

 glacial advances are sharply punctuated by the appearance and 

 disappearance of species. In America apparently such appearances 

 and disappearances are gradual. 



PRINCIPAL REFERENCES 



Deperet, Charles, "L'evolution des mammiferes tertiaires," Compt. Rend. 



Acad. Set., Paris, June 5, July 3, November 6, 1905, March 12, 1906. 

 OsBORN, H. F., "Correlation between Tertiary Mammal Horizons of Europe and 



America; an Introduction to the More Exact Investigation of Tertiary 



Zoogeography; Preliminary Study, with Third Trial Sheet," New York 



Acad. Sci. Ann., Vol. XIII (1900), pp. 1-64. 

 , "Cenozoic Mammal Horizons of Western North America," U. S. Geol. 



Sun'. Bull. j6i (1909), pp. 1-138. 

 Matthew, W. D., "A Provisional Classification of the Freshwater Tertiary of 



the West," Am. Mus. Nat. Hist. Bull, Vol. XII (1899), pp. 19-77. 

 , "Faunal Lists of the Tertiary Mammalia of the West," Appendix to 



"Osbom's Cenozoic Mammal Horizons of Western North America," U. S 



Geol. Surv. Bull. j6i, pp. 91-138. 

 Dall, W. H., " a Table of the North American Tertiary Horizons Correlated with 



One Another and with Those of Western Europe: with Annotations," U. S. 



Geol. Surv., i8th Ann. Rept. (1896-97), Part II, 1898. 

 , "Age of the Peace Creek Bone Beds of Florida," Acad. Nat. Sci. Phila. 



Proc. (1891), p. 121. 



