THE GENESIS AND MIGRATIONS OF PLANTS 221 



Before venturing on such extreme speculations as some now 

 current on questions of this kind, we would require to know 

 the successive extinct floras as perfectly as those of the modern 

 world, and to be able to ascertain to what extent each species 

 can change, either spontaneously or under the influence of 

 struggle for existence, or expansion under favourable conditions, 

 and under Arctic semi-annual days and nights, or the shorter 

 days of the tropics. Such knowledge, if ever acquired, it may 

 take ages of investigation to accumulate. In any case the sub- 

 ject of this paper indicates one hopeful line of study with 

 the object of arriving at some comprehension of the laws of 

 creation. 



While the facts above slightly sketched impress us with the 

 grand progress of the vegetable kingdom in geological time, 

 they equally show the persistence of vegetable forms as com- 

 pared with that of the dead continental masses and the decay 

 of some forms of life in favour of the introduction of others. 



When we find in the glacial beds the leaves of trees still 

 living in North America and Europe, and consider the vicissi- 

 tudes of elevation and submergence of the land, and of 

 Arctic and temperate climates which have occurred, we are 

 struck with the persistence of the weak things of life, as com- 

 pared with the changeableness of rocks and mountains. A 

 superficial observer might think the fern or the moss of a 

 granite hill a frail and temporary thing as compared with solid 

 and apparently everlasting rock. But just the reverse is the 

 case. The plant is usually older than the mountain. But the 

 glacial age is a very recent thing. We have facts older than 

 this. As hinted in a previous paper, in the Laramie clays 

 associated with the Lignite beds of North-western Canada 

 beds of Lower Eocene or early Tertiary age which were de- 

 posited before the Rocky Mountains or the Himalayas had 

 reared their great peaks and ridges, and at a time when the 

 whole geography of the northern hemisphere was different 



