The moon still revolved about the earth, but more slowly. Its distance from the earth had increased and its _apparent_ diameter had diminished. At the same time the period of the earth’s rotation had lengthened. This slower rotatory motion of the earth, increase in the distance of the moon, and lengthening of the lunar month, were the results of the friction of the tides, whose action resembled that of a brake. If the earth and the moon last long enough, and there are still oceans and tides, calculation would enable us to predict that the time would come when the periodic time of the earth’s rotation would finally equal the lunar month, so that there would be but five and one-quarter days in the year: the earth would then always present the same side to the moon. But this would require more than 150 million years. The period of which we are speaking, ten million years, is but a fifteenth of the above; and the time of the earth’s rotation, instead of being seventy times, was only four and one-half times greater than it now is, or about 110 hours. These long days exposed the earth to the prolonged action of the sun, but except in those regions where its rays were normal to the surface, that is to say in the equatorial zone between the two tropical circles, this exposure availed nothing; the obliquity of the ecliptic had not changed; the inclination of the axis of the earth being the same, about two degrees, and the changes in the eccentricity of the earth’s orbit had produced no sensible effect upon the seasons or the climate. The human form, food, respiration, organic functions, physical and intellectual life, ideas, opinions, religion, science, language—all had changed. Of present man almost nothing survived. [Illustration] [Illustration] CHAPTER IV. The last habitable regions of the globe were two wide valleys near the equator, the basins of dried up seas; valleys of slight depth, for the general level was almost absolutely uniform. No mountain peaks, ravines or wild gorges, not a single wooded valley or precipice was to be seen; the world was one vast plain, from which rivers and seas had gradually disappeared. But as the action of meteorological agents, rainfall and streams, had diminished in intensity with the loss of water, the last hollows of the sea bottom had not been entirely filled up, and shallow valleys remained, vestiges of the former structure of the globe. In these a little ice and moisture were left, but the circulation of water in the atmosphere had ceased, and the rivers flowed in subterranean channels as in invisible veins.