The Ocean of Ooze was a body of liquid on Skaro that separated the continents of Davius, the original home of the Thals, and Dalazar, the original home of the humanoid Daleks. (COMIC: Genesis of Evil)
Research by human historians of the Daleks uncovered creation myths about the Daleks in some of the cultures conquered by the Daleks, which mentioned the Ocean of Ooze as "a great Sea of Ooze". (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)
Behind the scenes
In Genesis of Evil, Skaro's two indigenous sentient species live on the continents of Dalazar and Davius, separated by the Ocean of Ooze. By the events of both Genesis of the Daleks and The Daleks, Thals, Kaleds and Daleks inhabited the same continent. The Secret Lives of Monsters offers partial explanation for the differences between stories. In the book, a Thal account of history states that until most life there was eradicated, the Thals previously lived on the continent of Darren, which was also occupied by the humanoid Daleks in Genesis of Evil. After the devastation, the surviving Thals settled on Davius until drought and failing crops forced them to relocate once again to Dalazar, where they discovered the Dalek City.