Blocks of cards secretly glued together for a methodological purpose are described by Carl Willmann in Die Zauberwelt, Vol. 4 No. 11, Nov. 1898, p. 166, in an effect called “Die Anziehungskraft der Erde” by Martignoni. In that effect, the cards of each half of the deck are glued together, making two fused blocks of cards. A selection is replaced between these blocks (after they have been switched in for a normal deck). When held loosely, the selection drops out when the deck is held upright. (Willmann describes another option to make the blocks: They can be sewn together in such a way that the blocks can still be slightly spread and riffled.)
The solid deck as a gag was described by Harry Hanaoka as “Frozen Cold Deck” in The Sphinx, Vol. 25 No. 6, Aug. 1926, p. 171. It was later popularized by Paul Harris as “Solid Deception” in Paul Harris Reveals Some of His Most Intimate Secrets, 1976, p. 1.