 Some have signs with certain patterns, but it is hard to classify them on the basis of engravings on the rock alone.Signs are conceptual expressions that are impossible to find in real life but are repeated expressions of a certain pattern.According to the results of an analysis of animal bones discovered in a shell midden in Ulsan and widespread along the southeastern coasts and of research on Ulsan Bay's archaeological environment, the site dates from 6,000 to 1,000 BC.