CHAPTER XVIII. SUCCESSION OF VEGETABLE LIFE. 



397 



We have stated that when the cold of the glacial epoch 

 moderated, the arctic plants that had invaded the temperate 

 zone mostly withdrew to the northward. But this is not true of 

 all. It is an interesting fact, that some of the remains of this 

 flora are still found on high elevations in temperate latitudes. 

 High up in the Alps and Pyrenees are found species which now 

 occur nowhere else in Europe, save in Scandinavia and Finland ; 

 and in the White Mountains of New Hampshire and the Green 

 Mountains of Vermont, as well as in portions of the Rocky 



Fig. 579. 



Mountains, lingers a flora that now finds its counterpart only in 

 Labrador and ether parts of northern British America. The only 

 satisfactory explanation for these facts is, that when the rigors 

 of the ice age began to relax and the ice-cap withdrew to its 

 native north, many cold-loving plants, instead of following it in 

 its retreat, found safety and a congenial temperature on these 

 mountain-tops. 



The accompanying diagram, Fig. 579, summarizes the most 

 important facts at present known regarding the chronology of 

 plants. The spaces between the horizontal lines represent geo- 

 logic periods, and the black areas in the vertical columns, the 

 beginning and increase or decrease of the principal types of 



