20 Canadian Record of Science. 
Columbia, form probably, a later flora brought into existence 
after the first upheaval of the great parallel chains of moun- 
tains there. Following on all of these older floras, but 
possibly contemporaneous in age with some of them, are 
the sub-arctic species now on the headlands of Lake Superior 
and the maritime plants presently on the shores of all of 
the Great Lakes. The most recent creations are without 
doubt those species—well represented by compositee— 
which frequent more especially the newer prairies of 
Manitoba. 
It is not difficult to see that the development of life on 
the earth from its dawn to the present, time has been largely 
influenced by the vast changes which have proceeded gra- 
dually but constantly throughout geologic time. In the 
Laramie age, which was a prolonged period, the great 
central plains of North America parallel to and east of the 
Rocky Mountains, and throughout much of the length of 
the continent, formed a vast, perhaps relatively, shallow 
inland fresh water sea; during and after the glacial times, 
whilst an equally great inland, ice-laden sea again prevailed 
over the northern central parts of the same continent, the 
southern portions were dry land. In later cretaceous and 
Kocene times, the climate of the sub-arctic regions was, 
relatively speaking, warm; in glacial times and since, it 
has deen so cold as to give a meaning of its own to the 
name arctic. During the tertiary times, the great dividing 
ridges forming the Rocky Mountains, were finally raised to 
their present elevations; whilst, as glacial times were 
passing away, the then much higher elevations and 
mountain ranges, which gave rise to the eastern glaciers 
of this period, were gradually lowered in elevation to what 
they appear at the present day. And these vast physical 
and climatic changes in tertiary and post-tertiary times are 
but an illustration of what has been going on from age to 
age from the very dawn of life upon the earth. What vast 
destruction of animals and plants each change must have 
occasioned! What a strugyle for existence must have 
taken place among those which were left! What adapta- 
tion to new conditions in which the survivors constantly 
