Introduction to the wonders of the ancient river bed: In the fourth layer of the cave, which is 36 meters above the modern underground river surface, there is a large area of ancient river bed sand and gravel deposits. The sediment layer has been corroded for many years and is distributed on the cave wall, forming large areas of white snow. The wonder of "rime"; on the section at the bottom of the cave, there are calcium slabs on the surface of the sand layer, new stalactites, goose tubes, buried small stalagmites and stone flags, etc., which are of great archaeological research value.