"1831 is titled Letter to Mr. - -"
The brackets are in the book and were made by T.O. Mabbott. The marginalia in green and blue ink are in Maureen Mabbott's hand.
As the note in the upper margin states, the photocopy comes from Mabbott's copy of the Harrison edition of Poe (1902). Harrison complicated matters by placing the SLM version among Poe's other prose introductions to his volumes of poetry instead of using "Letter to Mr. - - " as it appeared in Poems (1831).
Mabbott bracketed two passages on page 39 that were used in the notes of his version of "The Murders in the Rue Morgue." "As regards the greater truths" is quoted in note 29, and "He goes wrong by reason of his very profundity" is quoted in note 30. Both notes show us how Poe consistently argued that truth lies in surfaces rather than depths before he had Dupin echo his sentiments in "The Murders in the Rue Morgue."
Papers of Thomas Ollive Mabbott, Special Collections, University of Iowa Libraries; "The Murders in the Rue Morgue," in Collected Works of Edgar Allan Poe, Vol. II: Tales and Sketches, ed. Thomas Ollive Mabbott (Cambridge: The Belknap Press of Harvard University Press, 1978), 521-574.