As compensation for the lesser extent of dry land we may look forward to a more genial and favorable climate in the reduced areas that remain above water.
[Illustration: Fig.

3 .-- Relative Length of Ages of Reptiles, Mammals and Man.] _Length of Geologic Cycles._ But these vast cycles of geographic and climatic change will take millions of years to accomplish their course.

The brief span of human life, or even the few centuries of recorded civilization are far too short to show any perceptible change in climate due to this cause.

The utmost stretch of a man's life will cover perhaps one-two hundred thousandth part of a geologic period.
The time elapsed since the dawn of civilization is less than a three-thousandth part.

Of the days and hours of this geologic year, our historic records cover but two or three minutes, our individual lives but a fraction of a second.