1897.] Lhe Inferior Boundary of the Quaternary Era. 105 
era, even considered as synonymous with the term, “The Ice 
Age,” did not have glaciation as its predominating condition. 
In the light of modern discoveries in the later geologic history 
of Europe and America, the “ Glacial period ” becomes more 
figurative than real. Glaciation was the most remarkable and 
the most prominent feature of the Quaternary era, but its im- 
portance was not so great as to overshadow the claims of other 
natural conditions to the right of constituting the essential ele- 
ments in the definition and limitation of the era. 
It is the opinion of the present writer that the era whose 
early boundary is under discussion, was naturally set apart 
from all preceding time by a difference in climate, and toa 
less marked extent by a difference in fauna and flora; not so 
much by new species of animals and plants as by a different 
distribution of them. Just as the present climate differs from 
that of the Tertiaries so also differed the general Quaternary 
climate therefrom. We are, in fact, probably living under the 
normal conditions of the Quaternary era; at least there is no 
very important difference between the interglacial floral and 
faunal remains and those of the present time. But all of the 
various lines of research into the conditions prevalent in the 
Tertiary era, combine to demonstrate that its climate, in any 
given geographic district, was somewhat milder than in the 
same locality at the present time. It is the time of change 
from the mild Tertiary climate to the somewhat colder Quater- 
nary climate that I would consider as the most natural and, 
therefore, the most convenient divisional line between the two 
eras. 
In endeavoring to fix this time of climatic transition by 
means of the effects produced, we are confronted by the imper- 
fection of the geological record. A large part of the interval 
between the time of pronounced Tertiary mildness and early 
Quaternary severity, was occupied by conditions not favoring 
the preservation of organic remains, namely, by an elevated 
condition of the land and rapid erosion. Hence, we are 
reduced to the necessity of theoretically deducing the most 
probable cause of such a general change in climate, and then 
endeavoring to fix by evidence, if possible, the time when said 
cause or causes came into operation. 
