EXISTING VEGETABLE CREATION. 375 
youngest Alps, as is regularly the case with the more recent lava, nemst 
have been more tardily qualified for the growth of plants ; and, secondly, 
it is difficult to conceive that plants, found at present only at an 
elevation of 6,000 to 9,000 feet, should have been in existence at a 
time when there were no mountains of any such height, except, perhaps, 
at a distance whence migration was scarcely possible. Besides, how 
Shall we otherwise account for the actual presence of many plants 
peculiar to high Alps, though entirely wanting in the Apennines and 
Pyrenees, which have been raised at an earlier period? It must be 
admitted, nevertheless, that we cannot derive any very decisive argu- 
ment from the subsequent uplifting of the Alps, since we are in dark- 
ness regarding the period to which the present vegetable world extends, 
and likewise in how far it may have survived the vast convulsions 
caused by the uplifting of such vast chains of mountains. 
The decreasing warmth of the earth forms another ground for ascribing 
à young age to the flora of the Alps; for, if the earth has cooled gra- 
dually, those plants, which thrive only under the lowest degrees of 
temperature, must have been produced last, inasmuch as the climate 
favourable for their growth did not exist at an earlier period. The theory 
of Agassiz is, however, opposed to this view. According to him, there 
has been a period of our globe, preceding the present, in which not only 
Switzerland, but France and Germany, lay buried under a permanent 
covering of ice, like our polar regions. Against this theory may be 
fitly urged, among others, the frequent traces of trees, which occur 
in the north of Europe, in the most recent tertiary formations; and 
also the numerous indications of an arboreous vegetation in the oldest 
peat-formations, and the submarine forests, which point out that 
the diluvial period, or immediately after it, there existed an arbo- 
Teous vegetation in northern Europe, which assuredly could not have 
been the case had the middle of Europe been covered with perpetual 
snow. And, lastly, the fossil elephants and rhinoceroses of Siberia are 
opposed to the said theory ; for although it was a mistake to suppose 
that their presence was an indication of a warm climate, yet it is 
certain, on the other hand, that those animals could not have sub- 
_ Sisted where the soil was eternally covered with ice; and this must 
have been pre-eminently the case in the north of Europe and Siberia, 
had it existed in the middle of Europe. : 
It appears, then, that considerations even of climate plead in favour 
