Ages ago, a section of the Earth’s crust in the area that is now the Goto Islands was deformed (diastrophism), and part of a compressed layer of mudstone and sandstone was forced downwards. Bent in this way, parts of its upper surface broke off or were washed away due to erosion. What remained were the broken ends of the stratum that had descended into the earth. Here at Tatekojima Island you can see these broken ends protruding upwards almost vertically, and different layers of rock formed from deposits of mud and sand are easily visible.
Tatekojima is just a small outcropping of this geological stratum called the Goto Group, which is the subterranean foundation of the Goto Islands.
The rocky outline of Tatekojima appears to be separated from the mainland by a narrow channel. In fact, the channel is quite shallow, and when the tide is low the rocky spine connecting the main island of Fukue to Tatekojima becomes visible. If you time it correctly, you can walk from Fukue across the exposed rock to Tatekojima with just a pair of waterproof boots and explore millions of years of geological history for yourself.