(2.) _The development of the_ EARTH.--A dividing and sub-dividing of the original fluid going on would have evolved systems of various grades, and ultimately the orbs of space, among these the earth, an igneous sphere enveloped in vapors. (3.) _The production of the_ EARTH’S PHYSICAL FEATURES,--by the outlining of the continents and oceans. The condensible vapors would have gradually settled upon the earth as cooling progressed. (4.) _The introduction of_ LIFE _under its simplest forms_,--as in the lowest of plants, and perhaps, also of animals. As shown on page 396, the systems of structure characterizing the two kingdoms of nature, the _Radiate_ of the Vegetable kingdom, and the _Radiate_, _Molluscan_, _Articulate_, and _Vertebrate_ of the Animal, are not brought out in the simplest forms of life. The true _Zoic_ era in history began later. As plants are primarily the food of animals, there is reason for believing that the idea of life was first expressed in a plant. (5.) _The display of the_ SYSTEMS _in the Kingdoms of Life_,--the exhibition of the four grand types under the Animal kingdom, being the predominant idea in this phase of progress. (6.) _The introduction of the highest class of Vertebrates--that of the_ MAMMALS (the class to which MAN belongs), viviparous species, which are eminent above all other Vertebrates for a quality prophetic of a high moral purpose,--that of suckling their young. (7.) _The introduction of_ MAN,--the first being of moral and intellectual qualities, and one in whom the unity of nature has its full expression. There is another great event in the Earth’s history which has not yet been mentioned, because of a little uncertainty with regard to its exact place among the others. The event referred to is the first shining of the sun upon the earth, after the vapors which till then had shrouded the sphere were mostly condensed. This must have preceded the introduction of the Animal system, since the sun is the grand source of activity throughout nature on the earth, and is essential to the existence of life, excepting its lowest forms. In the history of the globe which has been given on page 196, it has been shown that the outlining of the continents was one of the earliest events, dating even from the Azoic age; and it is probable, from the facts stated, that it preceded that clearing of the atmosphere which opened the sky to the earth. This would place the event between numbers 3 and 5, and as the sun’s light was not essential to the earliest of organisms, probably after number 4. The order will, then, be-- (1.) Activity begun,--light an immediate result. (2.) The earth made an independent sphere. (3.) Outlining of the land and water, determining the earth’s general configuration. (4.) The idea of life expressed in the lowest plants, and afterward, if not contemporaneously, in the lowest or systemless animals, or Protozoans.