THE GENESIS AND MIGRATIONS OF PLANTS 205 



exaggerated by extreme glacialists, and while it is certain that 

 some vegetation, and this not altogether of Arctic types, con- 

 tinued to exist throughout this period, even in the now tem- 

 perate regions of our continents, it is evident that a great 

 reduction of the exuberance of the flora occurred by the 

 removal of many species, and that the present flora of the 

 northern hemisphere is inferior in variety and magnificence 

 to that of the Middle Tertiary, just as it is found that the 

 Mammalian fauna of our continents has since that time been 

 reduced both in the number and magnitude of its species. 



If the reader has followed this general sketch, he will be 

 prepared to appreciate some examples of a more detailed 

 character relating to the floras of different periods, and some 

 discussions of general points relating to the genesis and vicis- 

 situdes of the vegetable kingdom. 



The origination of the more important floras which have 

 occupied the northern hemisphere in geological times, not, 

 as one might at first sight suppose, in the sunny climates of 

 the South, but under the arctic skies, is a fact long known or 

 suspected. It is proved by the occurrence of fossil plants in 

 Greenland, in Spitzbergen, and in Grinnell Land, under cir- 

 cumstances which show that these were their primal homes. 

 The fact bristles with physical difficulties, yet is fertile of the 

 most interesting theoretical deductions, to reach which we may 

 well be content to wade through some intricate questions. 

 Though not at all a new fact, its full significance seems only re- 

 cently to have dawned on the minds of geologists, and within 

 recent years it has produced a number of memoirs and ad- 

 dresses to learned societies, besides many less formal notices. 1 



1 Saporata, "Ancienne Vegetation Polaire " ; Hooker, Presidential 

 Address to Royal Society, 1878; Thistleton Dyer, "Lecture on Plant 

 Distribution " ; Mr. Starkie Gardner, Letters in Nature, 1878, etc. The 

 basis of most of these brochures is to be found in Heer's " Flora Fossilis 

 Arctica." 



