CREATION BY EVOLUTION
because they yield the concentrated foodstuffs that made possible the evolution during Tertiary time of the mammals—the horses, cows, hogs, sheep, etc.—on which depend our agriculture and consequently our civilization.
The earliest floras of the Cenozoic era—the age of mammals and of flowering plants—are marked by a great modernization of forms. They consisted in large part of ancestors of forms that exist today, and their chief scientific interest lies largely in the great differences in geographical distribution which they show in contrast with the present distribution of their descendants. The contrast between the continents was not so great as in earlier times, and the whole Northern Hemisphere was clothed with forests much like those that survive today in southeastern Asia and southeastern North America. Species of magnolia, sequoia, walnut, and sassafras were then native in Europe, and during early Cenozoic time the nipa palm, the date, the cinnamon, and the bread fruit tree lingered in our Gulf States.
Gradually these floras become more modern; herbaceous plants—those having no persistent woody stem—multiplied, and then came another change of climate, during the epoch known to geologists as the Pleistocene. Because of the widespread glaciation which gives this epoch a distinctive place in geological chronology, it is often called the Ice Age or the glacial epoch, although a similar period of climatic rigor, already mentioned, occurred in Permian time, and evidence of other glacial epochs in early Paleozoic and pre-Paleozoic time has been discovered. Pleistocene glaciation was contemporaneous with the evolution of the human stock and exercised a profoundly modifying influence on the noble races of mammals and forest trees of the Northern Hemisphere. It also modified greatly the topography, pro-
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