436 ALPINE AND ARCTIC PLANTS 



materials of these mountains were accumulating, as beds of clay 

 and gravel, in the sea bottom. These were buried under great 

 depths of newer deposits, and were folded and crumpled by 

 lateral pressure, baked and metamorphosed into their present 

 crystalline condition. 1 Again heaved above the sea level, they 

 were hewn by the action of the waves to some degree into their 

 present forms, and constituted part of the nucleus of the 

 American continent in the later Tertiary period, when they were 

 probably higher than now. They were again, with all the sur- 

 rounding land, depressed under the sea in the Pleistocene 

 period, and in the Post-glacial or modern, slowly upheaved 

 again to their present height. These last changes are those that 

 concern their present flora, and their relations to it are well 

 stated by Sir C. Lyell in the following passages from his inter- 

 esting account of his ascent of Mount Washington in 1840. 



" If we attempt to speculate on the manner in which the 

 peculiar species of plants now established on the highest sum- 

 mits of the White Mountains were enabled to reach those 

 isolated spots, while none of them are met with in the lower 

 lands around, or for a great distance to the north, we shall find 

 ourselves trying to solve a philosophical problem which requires 

 the aid, not of botany alone, but of geology, or a knowledge of 

 the geographical changes which immediately preceded the 

 present state of the earth's surface. We have to explain how 

 an Arctic flora, consisting of plants specifically identical with 

 those which inhabit lands bordering the sea in the extreme 

 north of America, Europe and Asia, could get to the top of 

 Mount Washington. Now geology teaches us that the species 

 living at present on the earth are older than many parts of our 

 existing continents ; that is to say, they were created before a 

 large portion of the existing mountains, valleys, plains, lakes, 



1 While the mass of the White Mountains is probably older than the 

 Silurian, there are beds of mica schist which contain corals of the genus 

 Halysites, and stems of large crinoids. 



