It is to the heavens that we must look for our surest information on such a cosmic point, because of the long perspective other bodies give us of our own career. Less conclusive, because dependent upon less time, is any evidence our globe can offer. Yet even from it we may learn something; if nothing else, that it does not contradict the story of the sky. To it, therefore, we return, quickened in apprehension by the sights we have elsewhere seen.
The first thing our sharpened sense causes us to note is the spread of deserts even within historic times. Just as deserts show by their latitudinal girdling of the Earth their direct dependence upon the great system of planetary winds, as meteorologists recognizingly call them, so a study of the fringes of these belts discloses their encroachment upon formerly less arid lands. The southern borders of the Mediterranean reveal this all the way from Carthage to Palestine. The disappearance of their former peoples, leaving these lands but scantily inhabited now, points to this; because other regions, as India, which still retain a waterful climate, are as populous as ever. Much of this is doubtless due to the overthrow of dynasties and the ensuing lapse of irrigation, but query: Is it all? For we have still more definite information in the drying up of the streams which have left the aqueducts of Carthage without continuation, as much to water on the one hand as to its drinkers on the other. Men may leave because of lack of water, but water does not leave because of dearth of men to drink.
Recent search around the Caspian by Huntington has disclosed the like degeneration due to encroaching desertism there. Indeed, it is no chance coincidence that just where all the great nations thrived in the morning of the historic times should be precisely where populous peoples no longer exist. For neither increasing cold nor increasing heat is responsible for this, seeing that no general change has occurred in either. Nor were they particularly exposed to extermination by northern hordes of barbarians. Egypt as a world power died a natural death, and Babylonia too; but the common people died of thirst, indirect and unconscious and not wholly of their own choosing. Prehistoric records make this conclusion doubly sure, by lengthening the limit of our observation. Both extinct flora and extinct fauna tell the same tale. In the neighborhood of Cairo petrified forests attest that Egypt was not always a wiped slate, while the unearthed animals of the Fayum bear witness to water where no water is to-day.