When Izu Peninsula was a collection of submarine volcanoes several million years ago, the surrounding seabed had sediments of sand and volcanic ash. These sediments were shaped by the marine current over the years, leaving this beautiful intertwined pattern which we can now see on the strata in Bentenjima Island. Ancient current directions can be identified by studying the cross pattern on the rock. Due to this unusual twisted pattern, this cross lamina rock was very popular as building material in the Edo era.