The Moon Pool

The Moon Pool is a fantasy novel by American writer Abraham Merritt. It originally appeared as two short stories in All-Story Weekly: "The Moon Pool" (1918) and its sequel, "Conquest of the Moon Pool" (1919). These were then reworked into a novel released in 1919. The protagonist, Dr. Goodwin, would later appear in Merritt's second novel The Metal Monster (1920).

Although Merritt did not invent the "lost world" novel--he followed in the footsteps of Bulwer-Lytton, Burroughs, Conan Doyle, and others--this work extended the tradition. (wikipedia.org)