Of old, Heaven and Earth were not yet separated, and the In and Yo not yet divided. They formed a chaotic mass like an egg, which was of obscurely defined limits, and contained germs. The purer and clearer part was thinly diffused and formed Heaven, while the heavier and grosser element settled down and became Earth. The finer element easily became a united body, but the consolidation of the heavy and gross element was accomplished with difficulty. Heaven was therefore formed first, and Earth established subsequently. 'Thereafter divine beings were produced between them

(The Nihong)