MOSSES. 45 
stance would indicate that their original centre of 
distribution exists in these dreary regions, and 
that from thence they have been disseminated 
over the British and European mountains. The 
Alpine species are exceedingly restricted, seldom 
being found lower than 3000 feet, and often ascend- 
ing to a height of 4000 feet on the British hills, 
and 8000 feet on the Alps of Switzerland and the 
Pyrenees; the isothermal line of these altitudes 
corresponding with the plains of Lapland and 
the level of the sea-shore in the Arctic regions. 
Along with the small moss-like Alpine flowers 
with which they grow, they must have been wafted 
down to the Highland mountains, either as germs 
or as full-sized plants, growing undisturbed in 
their native soil, when these mountains existed as 
islands in the midst of an immense glacial sea 
which swept over what is now the continent of 
Europe. When this sea retired, owing to the 
elevation of the land, and its islands became 
mountain peaks and ranges, the tiny plants which 
imparted to them their first faint tinge of verdure 
still remained, finding the same conditions of 
temperature, shade, and moisture among the 
clouds as they formerly found on the shore of an 
icy sea. Thus all the Alpine plants found on the 
summits of our loftiest hills are Norwegian or 
Arctic species. They are besides the oldest living 
