Brown Study Meaning

(idiomatic, dated) A melancholy mood accompanied by deep thought; a moody daydream.

Example: 1851, Herman Melville, Moby-Dick:
  So gathering up the shavings with another grin, and throwing them into the great stove in the middle of the room, he went about his business, and left me in a brown study.
1893, Arthur Conan Doyle, "The Adventure of the Resident Patient":
  Finding that Holmes was too absorbed for conversation, I had tossed aside the barren paper, and leaning back in my chair, I fell into a brown study. Suddenly my companion's voice broke in upon my thoughts.
1978, Lawrence Durrell, Livia, Faber & Faber 1992 (Avignon Quintet), p. 428:
  But Quatrefages glared at his plate in a brown study.