44 Development and Distribution of Vegetation. 
the white elm and the white oak existed then, the monarchs of the forests, 
having all the characteristics of those of our day. The rich herbage was 
cropped by the deer and the buffalo which have descended without sensible 
change to us, while the monstrous mastodon, which accompanied them, has 
passed away. After the recession of the great ice sheet, 70,000 years ago, from 
the area which we inhabit, flowers of brilliant colors and sweet perfume decked 
the hill-sides and valleys and sweetened the air. Robins fed upon the berries 
of the wild grapevine and of the black cherry tree, and scattered far and wide 
the seeds over the continent so long ago that we should need to multiply the 
age of our nation by more than seven hundred times to express the years. It 
is true, that during this time many minor changes have occurred in the vege- 
tation of our country; but botanists compare the remains of these older 
plants and place them without hesitation in the genera and mostly in the 
species growing at present in our waste places and woodlands. The fact ‘is, 
70,000 years ago is modern time in the history of the world of plants. 
The causes of the cold and wonderful deposit of snow have been well 
worked out, but cannot be entered upon here. Our purpose is gained in call- 
ing attention to the fact and in noting the effect upon vegetation. It is to be 
understood that the whole northern hemisphere was involved in this paroxysm 
of cold. Though the ice did not push its way much south of 38° or 39° north 
latitude, its effects reached much further, how far we cannot say. 
Complete as the evidence of the glacial epoch is, the proof of a preceding 
warm period is equally convincing. Greenland is to-day a region of snow 
and ice. Except in favored localities the vegetation is confined to lichens and 
a few other kinds of low plants capable of resisting the cold of long winters 
and awaking to short periods of activity during the fitful presence of sunshine 
and warm air. But, buried in the rocks, there have been preserved the fos- 
silized remains of an abundant flora, embracing forest trees such as now thrive 
in our own latitude and southward — hickories, oaks, maples, magnolias, sassa- 
fras, the southern cypress, gum trees, and the giant redwoods of California. 
No better evidence can be asked for of the mild character of climate. These’ 
trees could not then, more than now, live in frigid regions. That they lived 
at all is sure testimony that the climate was what would be suitable to them 
now. ‘The species are indeed deemed to be different in most cases; but in 
some are so nearly identical that the closest comparison is required to detect 
the variation. No doubts are entertained as to their generic relations. In 
the ease of the bald cypress not even specific difference has been made out. 
The warm climate prevailed throughout the arctic region. The fossils from 
Nova Zembla and Spitzbergen tell the same story as do those from Greenland 
and Alaska. The whole northern hemisphere had an exceptionally high tem- 
perature. 
Like that of the glacial period the duration of the epoch of high tempera- 
ture covered hundreds of thousands of years and is explained by reference to 
astronomical and geographical conditions, combined in the opposite manner 
from what they were during the period of cold. 
DEVELOPMENT OF PLANTS DURING GEOLOGICAL AGES, 
We have seen that 80,000 years is a comparatively short period in the age of 
the vegetable world. If the limit of man’s years is three score and ten, then 
two and a half months corresponds in his age to 80,000 years in the life 
history of the vegetable kingdom as above estimated. If now we take this 
two and a half months in the period of adult vigor, how much change can be 
detected in the appearance of aman? Yet, we are familiar with the charac- 
teristic of infancy, of youth, of middle and of old age in human beings. So 
all that is necessary to find change in the world of plants, is to extend 
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