Lactustrine Deposits

20 mln years ago, before the Sea of Japan was formed, the land of Oki is thought to have been at the bottom of a huge lake. In the coastal areas of Dōgo Island, we can see sandstones and conglomerates that were deposited in lakes and rivers on the continental margin. Since they contain fossils of temperate climate plants such as jolcham oak, and animals—river snails and other freshwater shellfish, they tell us about the environment of Oki before the Sea of Japan was formed.