Minecraft wiki entry for Before_1.18, associated text: The swamp hills variant featured hillier terrain rising up between the flat marshes. These hills would tower over the otherwise low-elevation swamp. Additionally, flooded areas in swamp hills tended to reach lower depths than the rest of the swamp, sometimes deep enough to have a gravel floor in place of a dirt floor, like normal oceans. Swamp huts did not generate in swamp hills‌[Java Edition only], nor did slimes spawn, but fossils did still generate underground. Additionally, seagrass did not generate in flooded areas of swamp hills. If it connected to a jungle edge it had a chance to create a modified jungle edge biome.