But I am inclined to doubt whether the tradition of such local floods was ever preserved long enough to account for deluge-myths. All experience shows that the memory of historical events fades away with surprising rapidity when it is not preserved by written records. If, as Xenophon records, all memory of the great city of Nineveh had disappeared in 200 years after its destruction, how can it be expected that oral tradition shall preserve a recollection of prehistoric local floods magnified into universal deluges? And when the deluge-myths of different nations are examined closely, it generally appears that they have had an origin rather in solar myths or cosmogonical speculations, than in actual facts. For instance, the tradition of a deluge in Mexico has often been referred to as a confirmation of the Noachian flood. But when looked into, it appears that this Mexican deluge was only a part of their mythical cosmogony which told of four successive destructions and renovations of the world by the four elements of earth, air, fire, and water. The first period being closed by earthquakes, the second by hurricanes, the third by volcanoes, it did not require any local tradition to ensure the fourth being closed by a flood. Again, deluge-myths must have inevitably arisen from the presence of marine shells, fossil and recent, in many localities where they were too numerous to escape notice. If palæolithic stone implements and bones of fossil elephants gave rise to myths of thunderbolts and giants, sea-shells on mountain-tops must have given rise to speculations as to deluges. At the very beginning of history, Egyptian and Chaldæan astronomers were sufficiently advanced in science to wish to account for such phenomena, and to argue that where sea-shells were found the sea must once have been. Many of the deluge-myths of antiquity, such as that of Deucalion and Pyrrha, look very much as if this had been their origin. They are too different from the Chaldæan and Biblical Deluge, as for instance in repeopling the world by stones, to have been copied from the same original, and they fit in with the very general belief of ancient nations that they were autochthonous. In a majority of cases, however, I believe it will be found that deluge-myths have originated from some transmission, more or less distorted, of the very ancient Chaldæan astronomical myths of the passage of the sun through the signs of the zodiac. This is clearly the case in the Hindoo mythology, where the fish-god Ea-han, or Oannes, is introduced as a divine fish who swims up to the Ark and guides it to a place of refuge.