玄武洞

160万年前の火山活動でできた美しい柱状節理と等間隔の板状節理、地球磁場逆転を世界に先駆けて発見した場所、そして岩石名「玄武岩」の由来の場所、と地質好きであれば1度は訪れたいところ。洞になっているのは採石の跡だそうです。真っ直ぐの岩に垂直に切れ込みまで入っている岩を昔の人が重宝したのは納得です。（2018年5月）

Genbudo (Genbu Cave)

This is "must visit place" for geo lovers. The beautiful columnar and tabular joint were created by volcanic activity of 1.6M years ago. Matsuyama was the first to surmise "geomagnetic reversal” finding that rocks here and other locations were magnetized opposite. And Japanese name Geubu-gan(Basalt in English) were named after this place. The rocks were cut and used as material old days and the current hole(cave) is the remain.     (2018.May)