A MOUNT WASHINGTON SANDWORT. 593 



tricity drew nigh, the ice-cap began to form around the north pole. 

 From the Arctic Ocean, the great sheet of solid glacier descended over 

 Canada and the Eastern States till all New England, New York, and 

 Pennsylvania lay covered with five thousand feet thickness of un- 

 broken crystal. The ice cleared all animal and vegetable life off the 

 face of the earth wherever it rested, and drove before it the old arctic 

 fauna and flora as far south as Maryland, Virginia, and Kentucky. 

 After many minor chances and changes, however, brought about by 

 the recurrent cycles of summer and winter in the northern and southern 

 hemisphere alternately, the world's weather began slowly to improve 

 again. Step by step the ice retreated northward once more, till at last 

 only the comparatively insignificant polar cap remained to bear wit- 

 ness to its sway, with a few casual southern extensions, like the one 

 that still envelops all upper Greenland in its desolating sheet. As it 

 slowly retired, the arctic fauna and flora followed close in its rear, on 

 both sides of the Atlantic, till nowadays the plants and animals which 

 once covered the plains of Europe, Canada, and New England find 

 their last home in Spitzbergen, Nova Zembla, and the extreme north- 

 ern shores of British America. 



They left behind, however, some tokens of their presence to the 

 present day even in the lower latitudes of Europe and America. The 

 Greenland sandwort, among the New Hampshire hills, is just as much 

 a relic of the Glacial Epoch as the striated rocks, the erratic bowlders, 

 and the coarse drift which the Great Ice Age stranded high up the 

 slopes and corries of Mount Washington, where we still find them in 

 our own times. All the other glacial species (including that rare 

 White Mountain butterfly which occurs on the very summit of that 

 one peak, and nowhere else south of Labrador) have struggled on side 

 by side with it, in isolated colonies, from the days when the ice re- 

 treated northward to the present moment. But there is a great dif- 

 ference in this respect between Europe and America, as Dr. Asa Gray 

 has well pointed out. With us, in the Old World, great lateral ranges 

 of mountain — Alps, Pyrenees, Dovrefjeld, and Caucasus — still nourish 

 large existing glaciers and snow-fields, the lineal descendants of the 

 universal ice-sheet of the Glacial Epoch. Hence, our European mount- 

 ain flora, and, to a less extent, our mountain fauna as well, are even 

 now large and flourishing ; they retain a marked arctic appearance, 

 and recall all the well-known stunted features of the glacial assem- 

 blage of plants and animals. The' snowy mountain regions have acted 

 as continuous nurseries for the dwarfed vegetation of the Great Ice 

 Age. In America, on the other hand, you have few hills of any size 

 east of that great backbone of the continent, the Rockies, and none 

 of these hills rise to anything like snow-level. Hence, your mountain 

 flora is, on the whole, but a poor one, and most of the species are the 

 familiar kind which the European botanist already knows well among 

 the Swiss Alps and the Scotch Highlands. 



TOL. XXX. — 38 



