In another essay I tried to give a general view of the structure of the unconscious.
Its contents, the archetypes, are as it were the hidden foundations of the conscious mind, or, to use another comparison, the roots which the psyche has sunk not only in the earth in the narrower sense but in the world in general.
Archetypes are systems of readiness for action, and at the same time images and emotions.
They are inherited with the brain structure— indeed, they are its psychic aspect.
They represent, on the one hand, a very strong instinctive conservatism, while on the other hand they are the most effective means conceivable of instinctive adaptation.
They are thus, essentially, the chthonic portion of the psyche, if we may use such an expression—that portion through which the psyche is attached to nature, or in which its link with the earth and the world appears at its most tangible.
The psychic influence of the earth and its laws is seen most clearly in these primordial images. ~Carl Jung, CW 10, Para 53