Definition of "immemorially"

[…] by vast odds, the most terrific of all mortal disasters have immemorially and indiscriminately befallen tens and hundreds of thousands of those who have gone upon the waters […]

1851 November 14, Herman Melville, “Chapter 58”, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley

Yet, O reader, the brave woman accepted the lot, and took up the cry which had been its sign immemorially, and which thenceforward was to be her salutation without change—“Unclean, unclean!”

1880, Lew Wallace, Ben-Hur: A Tale of the Christ‎, Book Six, Chapter 2

[…] as for barbers, he had never liked those who cut his own hair; he thought too how it would disgust Pundit Jairam to learn that his former pupil had taken up barbering, a profession immemorially low.

1961, V. S. Naipaul, A House for Mr Biswas, Vintage International, published 2001, Part One, Chapter 2