 Eventually, subsequent to the period of his story, the two seas drain off into the Atlantic and the culture dependent on them decays and disappears, leaving only the remnant of Opar forgotten in the jungles where Tarzan will discover it.The seas' modern remnants are represented to be the much-shrunken Lake Chad and the Congo River basin.While originally derived from the Tarzan series, the world created by Farmer is given its own independent literary existence, with the sociological and cultural aspects worked out in meticulous detail, and a long historical annex added at the end.