462 RECENT ADVANCES IN GEOLOGY. 
and ornamented them with elaborate designs, and the human 
face, even, is portrayed with rare fidelity ; and finally, they 
must have maintained an intercourse with distant and widely 
separated portions of the continent. 
Since the close of the Reindeer Epoch the changes which 
have taken place in the flora and fauna of Europe have been 
slight. We may note, however, the disappearance of the 
Scotch fir (Pinus sylvestris) from Denmark, where it is 
found entombed in the peat-swamps, and the introduction of 
the sessile oak, which in turn is becoming supplanted by the 
common beecli. In the Baltic the oyster flourished in places 
from which it is now excluded, and certain other marine forms 
that attained a full growth, are now dwarfed. There is an 
instance or two of the disappearance of mammalian forms, 
but this may be traced to the direct agency of man. These 
slight changes in physieal geography have modified the dis- 
tribution of animals and plants, but they have not affected, in 
the least, their form. Whatever ehanges have been observed 
are due to domestication. 
So far as relates to our own country, there are evidences 
in the Great Basin and on the Colorado Plateau, that at no 
remote day there was a much more genial climate and a soil 
more productive than now prevail. This is seen in the dead 
forests that line the mountain side ; in the waterlines of the 
lakes and streams high above the greatest floods; deep 
eafions through which now course trickling streams, but 
which must have formed the channels of voluminous rivers; 
and alluvial bottoms now bare and desolate, in which are 
imbedded a robust vegetation. 
I have, perhaps, dwelt too long upon these changes which 
have so essentially modified the surface of the earth, and at 
the same time the destinies of our race. Had an Arctic cli- 
mate continued to prevail over what is now the temperate 
zone, man would have made no advance in civilization ; life 
to him would have been a continued struggle for existence. 
It is only in a genial climate, and on a soil so-generous as to 
