116 PHYSICAL GEOGRAPHY. 



through Kansas, Nebraska, Northwestern Iowa, Minnesota, Can- 

 ada, and is found to appear in Greenland. 



At the opening of the next, or Tertiary Age, in its lowest mem- 

 ber, the Eocene, it makes its appearance in the far north in Green- 

 land. Many of the species are identical with those now common 

 in Nebraska. It is true that Heer pronounces these to be Miocene,, 

 but Dawson has shown them to be of Eocene age. (Report on 

 Geological Survey of Canada.) By the time that the Miocene 

 age commenced, they were still among the conspicuous forms in 

 high northern latitudes. They emigrated southward with the 

 gradually advancing cold of the Pliocene Age, and when the Gla- 

 cial Age spread its mantle of ice over the north, they found a re- 

 treat in the southern United States and Mexico. At the final re- 

 treat of the glaciers, this Flora advanced northward, and found a 

 home in central North America. The nearest allies, therefore, of 

 our present Flora are the vegetable forms preserved in the rocks of 

 the Tertiary Ages, in high northern latitudes. All life, vegetable 

 and animal, probably commenced far north, and moved southward. 

 The old idea, that it must have originated in tropical regions, has 

 been eliminated from scientific belief by the advance of knowledge. 

 This view also accords best with what is known of the history of 

 the globe. The first known dry land was in high northern regions. 

 Arctic lands first became cool enough to sustain vegetable and ani- 

 mal life. (Heer.)* 



*See on this subject Gray's Forest Geography and Archaeology, Heer's Flora Fossilis Arc- 

 tica; Dawson's Reports on Canadian Geology; Saparta, "Ancieiine Vegetation Polairre"; 

 Hooker's Presidential Address to the Royal Society. 



