of the White Mountains, 89 



from this old mummy were at once recognised by Professor 

 Tuckerman as identical with this species, as it occurs on the 

 White Hills and on Katahdin in Maine. These facts are how- 

 ever easily explicable in comparison with those that relate to the 

 flowering plants. 



The spores of lichens and mosses float lighter than the lightest 

 down in the air, and may be wafted over land and sea, and drop- 

 ped everywhere to grow where conditions may be favourable. 

 Had the Egyptian embalmer used some of the first created spe- 

 cimens of Evernia furfuraeea, it might easily within the three 

 thousand years or so since his work was done, have floated round 

 the world and established itself on the White Hills. But, as we 

 shall see, neither the time nor means would suffice for the flower- 

 ing plants. The only available present agency for the trans- 

 mission of these would be in the crops or plumage of the migratory 

 birds ; and when we consider how few of these on their migra- 

 tions from the north could ever alight on these hills, and the 

 rarity of their carrying seeds in a state fit to vegetate, and further 

 that few of these plants produce fruits edible by birds, or seeds 

 likely to attach themselves to their feathers, the chances become 

 infinitely small of their transmission in this way. The most pro- 

 fitable course of investigation in this and most other cases of ap- 

 parently unaccountable geographical distribution, is to inquire as 

 to the past geological conditions of the region, and how these 

 may have affected the migrations of plants. 



The earlier geological history of these mountains far ante- 

 dates our existing vegetation. It belongs in the first instance to 

 the Lower Devonian period, in which the materials of these moun- 

 tains were accumulating, as beds of clay and gravel, in the sea 

 bottom. These were buried under great depths of newer de- 

 posits, and were baked and metamorphosed into their present 

 crystalline condition. 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 Ameri- 

 can continent in the tertiary period. They were again with all 

 the surrounding land depressed under the sea in the newer Plio- 

 cene period, and in the Post-pliocene 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 interesting ac- 

 count of his ascent of Mount Washington in 1846. 



