TERTIARY MAMMAL HORIZONS. 5 



while the parallels between Europe and America, or the ancient 

 Palaearctic and Nearctic Regions, have been discussed by Ger- 

 vAis, Leidv, Cope, Filhol, Scott, v. Zittel and Schlosser. 

 Lydekker has broadly covered the whole field in his Geo- 

 graphical Histoiy of Mammals. 



It may seem remarkable that a nearctic palaeontologist should 

 enter the palaearctic field, as the herald of a conference and 

 agreement upon common usage of terms, but I make no apol- 

 ogy because the matter arose from necessity rather than choice ; 

 several years ago the discovery of some new types of rhinoc- 

 eroses in this country directed my attention afresh to the study 

 of the Tertiary fauna of Europe as parallel with that of America, 

 in the succession of European and American types it appeared 

 that there were most interesting similarities between rhinoceroses 

 as widely separated as the present regions of Colorado and 

 southern France, but upon attempting more than a general com- 

 parison I was confronted by a lack of definite time scale be- 

 tween the levels in which these animals occur. The available 

 correlations by Cope, Filhol, Scott, y. Zittel and others 

 proved too indefinite at certain points. This difficulty became 

 so obstructive that a more exact correlation of European and 

 American horizons appeared to be an essential basis not only 

 for the phylogeny of the rhinoceroses but for that of other 

 types of mammals of Europe and North America. We need 

 a unified old world system as a starting point for comparison. 

 As a matter of fact there is even at the present moment no 

 consensus of opinion or common usage among palaearctic palae- 

 ontologists as to the larger divisions of the Tertiaiy. 



The Trial Sheets : — As an initial step towards a more ex- 

 act correlation I offer here a provisional clas.sification of the 

 Tertiary of Europe with critical discussion of the reasons for 

 placing the larger division lines at certain points, also a com- 

 parison chiefly with the Eocene of America, both accomplished 

 with as much aid from workers past and present as could be 

 mustered. This classification probably contains many errors, 

 some of them, perhaps, of a gross description. As I freely 

 criticise and differ from some of my colleagues, I trust they will 



