38 
ORIGIN OF LIFE IN AMERICA 
weight,” it once more permitted life from the south to move 
into the newly opened territory. The first wave of life, he 
thinks, which became dispersed over the glaciated region, as I 
have already mentioned above, was the barren-ground fauna 
and flora, the types of the far north. “ Hardly a trace,” 
he continues, “ now remains in the eastern United States of 
this pioneer class, and this class is now restricted to very 
limited areas or mountain top ‘ islands,’ as in the White 
Mountains. The present distribution of these arctic-alpine 
f islands ’ brings up a number of very interesting points. How 
is it that these alpine plants and animals are now found so far 
south and only upon high mountain peaks ? This question 
could not be rationally explained until the influence of the Ice 
Age upon life became recognised, and would, indeed, he a 
difficult one to answer if we did not take into consideration 
past conditions of climate and topography. We must recall 
that the arctic conditions which now occur outside of the arctic 
regions only on high mountain tops at that time extended to 
the very base of the mountains, and as the ice retreated to the 
north this cold zone gradually moved up the sides of the 
mountains carrying with it a characteristic flora and fauna. 
Thus with the retreat of the ice the first wave of life had 
two evident possibilities before it: first, to follow the ice 
north, or to follow the cold zone up the mountains. By this 
means small colonies of arctic plants and animals became 
separated from the main body of forms, and thus became 
alpine. To be sure, this segregation could only occur where 
the mountain peaks are isolated. If the mountains had been 
of sufficient height and had extended far to the north, a high¬ 
way would have been retained to the original stock, and thus 
the distribution would not have become discontinuous. From 
the above interpretation it seems fair to conclude that the 
arctic forms which now occur at alpine heights are relicts of 
the former widespread glacial fauna and flora, whose dis¬ 
tribution has become discontinuous by a change of climate.” 
Very similar ideas were held by Mr. Grote.* He thought 
the White Mountain butterfly (Oeneis semidea) was pushed 
southwards by the advance of the great northern ice-sheet. 
* Grote, A. R., “ Effect of Glacial Epoch,” p. 441. 
