The river represents some movement of the consciousness.
There are two movements — one an ascension of the lower consciousness to meet the higher, the other the descent of the higher consciousness into the lower. What you first experienced was an uprush of the lower consciousness from all parts so strong as to break the lid of the inner mind, that was the splitting of the skull and to enable the going of the two consciousnesses above to be complete. The result was a descent. Usually the first thing that descends from the higher consciousness is its deep and entire peace, the second is the Light, here the white light of the Mother. When the higher consciousness descends or is intensely felt, there is usually an opening of the limited personal being into the cosmic consciosness — one feels a wide and infinite being which alone exists, the identification with the body and even the sense of the body disappears, the limited personal consciousness is lost in the Cosmic Existence. You had all this first in the impersonal way; but after the burning up of the psychic fire, you felt the Personal wideness, the cosmic consciousness of the Divine Mother and received her blessing.