12 BERRY— A POSSIBLE EXPLANATION 



showing the supposed distribution of land and water in mid-Eocene 

 time.* 



It will be noted first that the land areas are greatly reduced, 

 amounting to perhaps as much as 40 per cent, of the present land 

 area of the Northern Hemisphere ; and their place is taken by mostly 

 shallow seas in low latitudes. The Mediterranean regions of the 

 world are almost continuously under water, and these have free polar 

 connections from the Atlantic, Pacific, and Indian oceans, as well as 

 from the greatly expanded Tethys. If the reader will now consult 

 Sir John Murray's quantitative estimates of the present influence of 

 the Gulf stream on western Europe, it will be obvious that a distribu- 

 tion of land and water such as I have indicated for mid-Eocene time 

 would be most important in climatic results. These effects would be 

 cumulative, and, in my opinion, a sufficient cause to account for the 

 observed distribution of the fossil floras of the upper Eocene. That 

 it is a matter of distribution of land and water plus oceanic circulation 

 is indicated by the more northern Eocene distribution of plant types 

 of low latitudes in Europe than in North America, as at the present 

 time. 



I would imagine a certain lag in observable effects, due to this 

 cumulative action, and the progressive reduction of polar ice, and the 

 ultimate nullification of appreciable cold ocean currents. I have indi- 

 cated on the map, in a most general way, the probable directions of 

 the oceanic circulation, as well as the localities where Eocene plants 

 have been found in high latitudes. No one knows exactly what paths 

 a given geographic pattern would impose on definite ocean currents, 

 there being so many factors involved ; but certainly no one can object 

 to the statement that the general, or what might be termed the plane- 

 tary circulation would dominate, except as modified by subordinate 

 and unvaluated factors; or that the northward drift of warm surface 

 waters would be operative. 



It will be noted that all of the most northern Eocene plant locali- 

 ties are in coastal situations, favorably situated to receive the full 



* This map makes no pretense to accuracy, which is largely a matter of 

 opinion, nor is there anything original about it. It is essentially the map 

 compiled from De Lapparent's " Traite " by W. D. Matthew, and used by H. 

 F. Osborn in his " Age of Mammals." 



