"The unconscious contains, as it were, two layers: the personal and the collective. The personal layer ends at the earliest memories of infancy, but the collective layer comprises the preinfantile period, that is, the residues of ancestral life.
Whereas the memory-images of the personal unconscious are, as it were, filled out, because they are images personally experienced by the individual, the archetypes of the collective unconscious are not filled out because they are forms not personally experienced.
When, on the other hand, psychic energy regresses, going beyond even the period of early infancy, and breaks into the legacy of ancestral life, the mythological images are awakened: these are the archetypes. An interior spiritual world whose existence we never suspected opens out and displays contents that seem to stand in sharpest contrast to all our former ideas."
-C.G. Jung, CW 7, par. 118