ORIGIN OF WHITE MOUNTAIN FAUNA 
39 
On the decline of the ice-sheet the butterflies turned north¬ 
ward, again returning to their native home. Some of the 
specimens strayed by the way and were destined to plant 
colonies apart from their companions as, for example, on the 
White Mountains. 
Botanists entertain analogous views. Dr. Harshberger * 
argues that the tundra vegetation and other arctic species 
of plants occupied during the Glacial Epoch the southern 
margin of the great ice-sheet, and that when most of them 
migrated north, on the disappearance of the ice, some re¬ 
mained behind to form the vegetation of sphagnum bogs and 
alpine summits of the higher mountains. 
If these theories are correct, the Asiatic invasion and the 
much more insignificant one from Europe, of which Helix 
hortensis is one of the most striking representatives (p. 13), 
should both be more recent than the flora and fauna of the 
White Mountains, for the former have n6t penetrated beyond 
the lower slopes of these mountains. 
Helix hortensis does not occcur nearer the White Mountains 
than Portland in Maine, which is fully seventy miles to the 
east. I have traced Oniscus asellus, a wood-louse probably 
belonging to the same group, as far as the base of the White 
Mountains. The earth-worm, Lumbricus castaneus, which 
seems to have spread from continental Europe to the Faroes 
and Iceland, reappearing on the other side of the Atlantic 
in Canada and New England, may be a member of the same 
dispersal. At any rate, I feel sure there are a great many 
more of such species that have not spread to the higher parts 
of the White Mountains, and therefore proclaim themselves as 
more recent immigrants than those which are now in posses¬ 
sion of the high plateau referred to. The latter are likewise 
clearly older than the Asiatic immigrants, which will be more 
fully described later on. 
But since Helix hortensis occurs in the lower Pleistocene 
clays of Maine, it, as well as the whole group of European 
immigrants, are pre-Glacial in age, and in this opinion I 
concur with several of the authorities who have discussed, 
this problem (p. 14). The members of this group arrived 
* Harshberger, John W., “ North American Plant Dispersal,” p. 2.. 
