Human intelligence had so completely mastered the forces of nature that it seemed as if so glorious an era never could come to an end. The decrease in the amount of water, however, commenced to alarm even the most optimistic. The great oceans had disappeared. The crust of the earth, once so thin and mobile, had gradually increased in thickness, and, notwithstanding the internal pressure, the earth had become almost completely solidified. Oscillations of the surface were no longer possible, for it had become entirely rigid. The seas which remained were confined to the tropics. The poles were frozen. The continents of olden times, where so many other foci of civilization had shone so brilliantly, were immense deserts. Step by step humanity had migrated towards the tropical zone, still watered by streams, lakes and seas. There were no more mountains, no more condensers of snow. [Illustration: “RUDIMENTARY SPECIES OF CRYPTOGAMS ONLY SURVIVED.” ] As the quantity of water and rainfall diminished, and, as the springs failed and the aqueous vapor of the atmosphere grew less, vegetation had entirely changed its aspect, increasing the volume of its leaves and the length of its roots, seeking in every way to absorb the humidity necessary for life. Species which had not been able to adjust themselves to the new conditions had vanished; the rest were transformed. Not a tree or a plant with which we are familiar was to be seen. There were no oaks, nor ashes, nor elms, nor willows, and the landscape bore no resemblance to that of today. Rudimentary species of cryptogams only survived. Like changes had taken place in the animal kingdom. Animal forms had been greatly modified. The wild species had either disappeared or been domesticated. The scarcity of water had modified the food of herbivora as well as carnivora. The most recent species, evolved from those which preceded them, were smaller, with less fat and a larger skeleton. The number of plants had sensibly decreased. Less of the carbonic acid of the air was absorbed, and a proportionally greater quantity existed in the atmosphere. As for the human race, its metamorphosis was so absolute that it was with an astonishment bordering on incredulity that one saw in geological museums fossil specimens of men of the twentieth or one hundredth century, with great brutal teeth and coarse intestines; it was difficult to admit that organisms so gross could really be the ancestors of intellectual man. Though millions of years had passed, the sun still poured upon the earth almost the same quantity of heat and light. At most, the loss had not exceeded one-tenth. The only difference was that the sun appeared a little yellower and a little smaller.