Young Folks' Library, Volume XI…
“ As the historian recognizes Ancient History, the Middle Ages, and Modern History as distinct phases in the growth of the human race, so they distinguished between what they called the Primary period, when, as they believed, no life stirred on the surface of the earth; the Secondary or middle period, when animals and plants were introduced, and the land began to assume continental proportions; and the Tertiary period, or comparatively modern geological times, when the physical features of the earth as well as its inhabitants were approaching more nearly to the present condition of things. ”
