8 



CENOZOIC MAMMAL HORIZONS 



statement of the important facts which led to its discrimination and of the charac- 

 teristics by which it may be identified in the field, whether by geologist or layman. 



As uniform conditions of deposition were local as well as temporary, it is to be 

 assumed that each formation is limited in horizontal extent. The formation should 

 be recognized and should be called by the same name as far as it can be traced and 

 identified by means of its lithologic character, its stratigraphic association, and its 

 contained fossils. 



The Surve}^ has a committee on geologic names, which considers 

 all questions of nomenclature that are raised by every paper offered 

 for publication. The matter now stands as follows: 



1 . According to the ruling of the Survey all formations shall receive 

 geographic names. 



2. The necessity for this rule is demonstrated in the present review, 

 because no two formations are found which are altogether coincident 

 in time, although they may partly or very largeh^ overlap in time. 



3. Both formation and faunistic names are more or less subject to 

 the law of priority of definition; but it is considered desirable by the 

 committee on geologic names that certain names which are appro- 

 priate and have become well established in the literature should be 

 retained, although their meanings may be preoccupied technically by 

 other names w^hich have not come into such general use. 



CORRELATION. 



The correlation of the Tertiary mammal horizons of western North 

 America with those of Europe has engaged the attention especially 

 of Cope (1879, 1884), Scott (1887), Clark (1891, 1896), Ball (1890, 

 1897), and Osborn (1897, 1898, 1900). As exact correlation appeared 

 to be an essential for the writer's phylogenetic studies of the rhinoc- 

 eroses and other groups, he published in 1897 a Trial sheet of the 

 typical and homot axial horizons of Europe" as the basis of coopera- 

 tion with various European geologists. Their kind criticisms and 

 corrections were embodied in a Second trial sheet" (1898) and in a 

 '^Third trial sheet" (1900). 



In the years 1899 and 1900 the writer gave two addresses « before 

 the New York Academy of Sciences, entitled ^^Correlation between 

 Tertiary mammal horizons of Europe and America" and ^'Faunal 

 relations of Europe and America during the Tertiary period and 

 theory of the successive invasions of an African fauna into Europe." 

 In 1899 Dr. W. D. Matthew published '^A provisional classification of 

 the fresh-water Tertiary of the West."^ In June, 1905, there began 

 in the Comptes Rendus a series of papers by Prof. Charles Deperet, 



a Osborn, H. F., Correlation between Tertiary manunal horizons of Europe and America; an introduc- 

 tion to the more exact investigation of Tertiary zoogeography; preliminary study, with third trial 

 sheet: Ann. New York Acad. Sci., vol. 13, No. 1, July 21, 1900, pp. 1-64. 



Osborn, II. F., Correlation des horizons demammiferes tertiairesen Europe et en Amerique: Conipt. 

 Rend. 8^ Cong. geol. intern., 1900, pp. 357-363. 



bBuU. Am. Mus. Nat. Hist., vol. 21, 1899, pp. 19-75. 



