422 Wbrtman — Studies of Eocene Mammalia in the 



Bpecies Populus primoeva, which is probably the oldest Angio- 

 sperm thus far discovered. 



In such distant localities within the Polar regions as Spitz- 

 bergen and Alaska are found deposits of nearly or quite the 

 same age, and here the same or a closely allied flora occurs. 

 The conclusion is therefore obvious that the climatic condi- 

 tions by which this plant life was surrounded were not confined 

 to a single locality and were not the result of local changes, 

 but this evidence compels us to believe that they were wide- 

 spread and general over the whole Arctic region during this 

 period. The mean temperature indicated by these plants, 

 according to Heer,* than whom no better authority could be 

 quoted, was from 21° to 22° C, or 70° to 72° F. this brings 

 it very near the isothermal line 74° F., which separates the 

 subtropical from the tropical temperature ; hence the climate 

 may be said to have been virtually tropical. 



Deposits corresponding closely in age to that of the Upper 

 Cretaceous of Europe and North America are found in the 

 same latitude., near the same locality as that just described. 

 These beds— the Atane — have furnished the remains of a flora no 

 less remarkable than that of the Lower Cretaceous- In all, sixty- 

 five species have been identified, of which fifteen are Ferns, 

 two Cycads, eleven Conifers, three Monocotyledons, and thirty- 

 four Dicotyledons. Of the Ferns, one is a Tree-Fern, which, 

 with the Cycads and other species, at once gives a subtropical 

 aspect to the flora. The Dicotyledons include such types as 

 the Poplars, Bay berry and Sweet Fern, Fig, Sassafras, Heath, 

 Cinnamon, Persimmon, Aralia or Ginseng, Magnolia, Myrtle, 

 and Legumes. The living representatives of many of these 

 species are now found in a subtropical or warm temperate 

 climate, and if such evidence has any value it furnishes incon- 

 testable proof that the temperature of the' Arctic regions, 

 although still tropical, had suffered a decline from that of the 

 Lower Cretaceous during the latter part of the period. 



Turning next to the Tertiary, we find from the same class of 

 evidence that wide-spread changes in the climatic conditions 

 had occurred. There are deposits at many localities within' 

 the Arctic regions in which plant remains of this epoch are 

 found, but their exact equivalents among European and 

 American beds are difficult of determination. They were 

 referred by Heer to the Miocene, but Dawson expressed the 

 opinion that they were at least in part Eocene in age — a view 

 which is more likely the correct one. Further exploration and 

 the discovery of animal remains are necessary before these 

 matters can be finally cleared up. At all events, it is perfectly 



* See Professor Heer's famous work, Flora Fossilis Arctica. 



