Out of Time's Abyss is a fantasy novel by American writer Edgar Rice Burroughs. The novel is a direct sequel to The Land That Time Forgot and The People That Time Forgot, continuing the lost world saga begun in the earlier stories.

It connects the previous two installments, bringing in characters introduced in each. Burroughs completes the revelation of his lost world's unique biological system, only hinted at in the previous installment, in which the slow progress of evolution in the world outside is recapitulated as a matter of individual metamorphosis. This system forms a thematic element serving to unite the three Caspak stories.

The Caspak trilogy was first published in Blue Book Magazine as a three-part serial in the issues for September, October and November 1918, with this short novel being the third and final installment. The complete trilogy was later combined for publication in book form in 1924 under the title The Land That Time Porgot. E-book: ePUB, 35 700 words, reading time approximately 3 hours. AUDIO: Reading by Ralph Snelson,  running time: 3 hours, 41 min. Unabridged full version. 

Edgar Rice Burroughs (1875-1950) was an American author, best known for his creation of the jungle hero Tarzan and the heroic Mars adventurer John Carter, although he produced works in many genres.