The so-called Honshu arc, the main part of Japan, was formed as the result of a ‘peri-Japan-Sea’ tectonic movement. The arc is divided geologically into two parts north-eastern and south-western Japan, by a line drawn from Itoigawa to Shizuoka. The Noto Peninsula and Sado Island, which are similar in form and on the concave side of the arc, were both elevated by this movement.
At the eastern end of South-Eastern Japan, we observe several mountain ranges arranged en échelon. The uplift of the Kaga-Mino range extends northwards and joining that of the peri-Japan-Sea movement, formed the great Noto Peninsula. At Sado Island, however, the two blocks that compose the island were elevated parallel with the tectonic features of the main part of the Honshû arc. Therefore Sado has remained an island.
In consequence of periodical uplifts of land, a step-like topography is developed extensively in the two districts. These steps are wider on the peninsula than on the island, but are at higher levels on the island than on the peninsula.
