42 Development and Distribution of Vegetation. 
time the imperial command went forth: ‘Let the waters under the heavens 
be collected together unto one place and let the dry land appear.” 
America and Asia were probably connected at what is now Behring’s straits, 
but otherwise these great land masses have had, not only an existence from 
the beginning of continental formations, but a separate existence during all 
time with the mighty stretches of the Pacific between them. It is also pre- 
sumable that land connection existed in the Tertiary period, or before, be- 
tween North America and Europe, where there is now a vast expanse of shal- 
low sea from Greenland, Iceland, the Faroe islands and Great Britain. That 
England joined the continent is undoubted. 
The northern hemisphere has ever been the land hemisphere, the southern 
what it is now,—vast expanses of water. 
We cannot now pause for the proof of these conclusions, but the evidences 
of the general stability of the great and characteristic geographical features 
of our earth are too abundant and too strong to admit other inferences. With 
much change of detail, with numerous oscillations of level, with upheavals 
and denudations, astonishingly great in themselves, but of little comparative 
effect, the great continental masses and the vast ocean areas are to-day what 
they were before the organic world had an existence, and what they have 
ever since continued to be. In an account therefore of the migration of 
plants we are not at liberty to suppose that the geographical world has ma- 
terially changed since this migration begun. 
THE AGE OF THE WORLD. 
The age of the world is a problem which has attracted much attention 
among those best able to solve it. Conclusions have however widely varied. 
No one conversant with geology now pretends to limit the six creative peri- 
ods, called days in the first chapter of Genesis, to twelve or to twenty-four 
hours of time each. Indeed it is impossible from the account itself to strictly 
interpret the term in this manner. 
The “‘evening” and the “‘ morning,” that is, from the evening to the morn- 
ing, constitutes for instance the first day. In a literal interpretation we 
should say this must have been night not day. But if we say the evening 
was the end of a period and the morning was the beginning of another, then 
we have the evening and the morning taken together as the division between 
the two. Eighteen hundred and seventy-six is the evening of British rule, 
and the morning of republican government in our country. No attempt can 
be here made to discuss what has been called the Mosaic cosmogony; but we 
must insist that the Earth with its prairies and forests, its green herbage and 
its maturing seeds, its fragrant flowers and luscious fruits, is many, very many 
times more than six thousand years old. We cannot reckon in years the age 
of the world. We know it has a definite age; but the measure of it has not 
been satisfactorily ascertained. Lyell estimates 240,000,000 years, and Pro- 
fessor Haughton on another basis 200,000,000 years as the time passed since 
the deposition of the earliest sedimentary rocks. Darwin says: ‘ Before the 
lowest Cambrian stratum was deposited, long periods elapsed—as long as, 
and probably far longer than, the whole interval from. the Cambrian age to 
the present day; and during these vast periods the world swarmed with living 
creatures.” His estimate of the time from the beginning of the Cambrian 
rocks is 300,000,000 years. Huxley is inclined to fix a greater age than this, 
and named the inside number 500,000,000 years. 
But the physicists reckon less time. Sir William Thomson says 100,000,000 
and Hembholtz 20,000,000, while Newcomb estimates but 10,000,000 years. 
Wallace, taking advantage of preceding discussions, and weighing all the evi-. 
dence concludes that the length of time elapsed since the deposition of the 
