An “ineffable” sighting

From The Four Quartets: "The Dry Salvages" by T.S. Eliot:

    It seems, as one becomes older,
That the past has another pattern, and ceases to be a mere sequence—
Or even development: the latter a partial fallacy
Encouraged by superficial notions of evolution,
Which becomes, in the popular mind, a means of disowning the past.
The moments of happiness—not the sense of well-being,
Fruition, fulfilment, security or affection,
Or even a very good dinner, but the sudden illumination—
We had the experience but missed the meaning,
And approach to the meaning restores the experience
In a different form, beyond any meaning
We can assign to happiness. I have said before
That the past experience revived in the meaning
Is not the experience of one life only
But of many generations—not forgetting
Something that is probably quite ineffable:
The backward look behind the assurance
Of recorded history, the backward half-look
Over the shoulder, towards the primitive terror.