of the White Mountaim. 91 



sporules of the fungi, lichens, and mosses, may be wafted through 

 the air for indefinite distances like smoke ; and in fact heavier 

 particles are actually known to have been carried for thousands of 

 miles by the wind. But the cause of the occurrence of Arctic 

 plants of the Phoenogamous class on the top of the New Hamp- 

 shire Mountains, specifically identical with those of remote polar 

 regions, is by no means so obvious. They could not in the pre- 

 sent condition of the earth affect a passage over the intervening 

 lowlands, because the extreme heat of summer and cold of win- 

 ter would be fatal to them. We must suppose, therefore, that 

 originally they extended their range in the same way as the 

 plants now inhabiting arctic and antarctic lands disseminate them- 

 selves. The innumerable islands in the polar seas are tenanted 

 by the same species of plants, some of which are conveyed as 

 seeds by animals over the ice when the sea is frozen in winter, or 

 by birds ; while a still larger number are transported by floating 

 icebergs, on which soil containing the seeds of plants may be 

 carried in a single year for hundreds of miles. A great body of 

 geological evidence has now been brought together to show that 

 this machinery for scattering plants as well as for carrying erratic 

 blocks southward, and polishing and grooving the floor of the 

 ancient ocean, extended in the western hemisphere to lower lati- 

 tudes than that of the White Mountains. When these last still 

 constituted islands in a sea chilled by the melting of floating ice, 

 we may assume that they were covered entirely by a flora like 

 that now confined to the uppermost or treeless region of the 

 mountains. As the continent grew by the slow upheaval of the 

 land, and the islands gained in height, and the climate around 

 these hills grew milder, the Arctic plants would retreat to higher 

 and higher zones, and finally occupy an elevated area which 

 probably had been at first or in the glacial period, always covered 

 with perpetual snow. Meanwhile the newly formed plains around 

 the base of the mountain, to which northern species of plants 

 could not spread, would be occupied by others migrating from the 

 south, and perhaps by many trees, shrubs, and plants, then first 

 created, and remaining to this day peculiar to North America." 



The time to which the above views of Sir C. Lyell would refer 

 the migration of the White Mountain flora, is historically very re- 

 mote. The changes of level which have submerged the American 

 continent and re-elevated its land, have occupied long periods. 

 Whether with Lyell we measure these periods by the recession 



