216 THE GEOLOGICAL HISTORY OF PLANTS. 



irrespective of stratigraphical considerations, the subject 

 lost its geological importance. But, when a good series 

 has been obtained in any one region of some extent, the 

 case becomes different. Though there is still much im- 

 perfection in our knowledge of the Cretaceous and Ter- 

 tiary floras of Canada, I think the work already done is 

 sufficient to enable any competent observer to distinguish 

 by their fossil plants the Lower, Middle, and Upper Cre- 

 taceous, and the latter from the Tertiary ; and, with the 

 aid of the work already done by Lesquereux and New- 

 berry in the United States, to refer approximately to its 

 true geological position any group of plants from beds of 

 unknown age in the West. 



An important consequence arising from the above 

 statements is that the period of warm climate which 

 enabled a temperate flora to exist in Greenland was that 

 of the later Cretaceous and early Eocene rather than, as 

 usually stated, the Miocene. It is also a question admit- 

 ting of discussion whether the Eocene flora of latitudes 

 so different as those of Greenland, Mackenzie Eiver, north- 

 west Canada, and the United States, were strictly con- 

 temporaneous, or successive within a long geological 

 period in which climatal changes were gradually pro- 

 ceeding. The latter statement must apply at least to 

 the beginning and close of the period ; but the plants 

 themselves have something to say in favour of contem- 

 poraneity. The flora of the Laramie is not a tropical 

 but a temperate flora, showing no doubt that a much 

 more equable climate prevailed in the more northern 

 parts of America than at present. But this equability 

 of climate implies the possibility of a great geographical 

 range on the part of plants. Thus it is quite possible 

 and indeed highly probable that in the Laramie age a 

 somewhat uniform flora extended from the Arctic seas 

 through the great central plateau of America far to the 

 south, and in like manner along the western coast of 



