01 / Geology
Rock formed 20–30 km undergroundsurfaces by the river.

The rock of Iwadatami (岩畳, "rock tatami") is crystalline schist, formed when seabed sediments were pushed some 20–30 km underground. Because it can be seen here at the surface, Nagatoro is called a "window on the Earth" (地球の窓). Researchers and students have kept coming since Dr. Edmund Naumann visited in 1878, and Chichibu-Nagatoro is known as the "birthplace of Japanese geology" (日本地質学発祥の地).
- Formed some 20–30 km underground
- Visited by Dr. Naumann, 1878
- Birthplace of Japanese geology

