Hence it was that when Bau assumed the dress of a Semitic goddess, she became first the creatress-mother, and then the mother of the creator. As such, however, she entered into rivalry with another deity who was similarly in process of development out of an earlier form. This was Zi-Kum or Zi-Garum, "the spirit of the sky," who is called "the mother that has begotten heaven and earth," and "the seeress of the spirit of the earth" (_Ê-kur_), that is to say, of En-lil.(238) To the primitive seafarer of Babylonia the waters of the Persian Gulf seemed to descend from the vault of heaven which rested upon them; the streams which intersected the ground were fed by the rains, and it was therefore natural to suppose that the sea which blended with the sky was similarly derived from it. The deep was embosomed in the heavens, and the spirit of the deep accordingly must have been begotten by the spirit of the sky.
But this spirit of the sky necessarily owned obedience to the "lord of the ghost-world," and the mother of Ea of Eridu was thus at the same time a ministering handmaid of En-lil.(239) The Zi who was worshipped at Eridu was also a Lil in the theology of Nippur, and the home of the Lil was beneath the earth. In this way we must explain how it is that Zi-Kum, "the heaven," is also, under another aspect, Zi-Kura, "the earth," and as such identical with Dam-kina and Bau.(240) That she should have coalesced with Bau rather than with Dam-kina, was due to the fact that the one was made the mother of Ea, while the other became his wife. But the lineaments of the old "spirit of the sky" were soon obliterated. As the religion of Babylonia moved further and further away from the animism of the past, the spirit's existence faded into the background and Bau stepped into its place. Zi-Kum, "the spirit of the sky," ended by becoming a symbol of that primordial deep from which Ea had derived his wisdom, and whose waters were above the visible firmament as well as below it.(241) Ea, the god of the mixed Babylonian race, had absorbed the spirits and ghosts of the Sumerian faith. Their attributes had been taken from them, and they had been transformed into goddesses whose sole end was to complete the family of the culture-god.