Abstract
The eastern verge of Fossa Magna has been defined by-various lines. NAUMANN considered a line connecting Naoetsu, Iwamurata, Wakamiko and Odawara as the verge. Currently, the verge extends to a line connecting Kashiwazaki and Choshi. Among the lines, the Iwamurata-Wakamiko line is a western verge fault of an old crustal block which formed when the sea of Tertiary period divided Honshu. Many grassy plains or grasslands exist along this line. A 30km-diameter plain between Mt. Tairappyousan and Mt, Makihatayama is a roof pendant which was raised by an intrusive granite formed at the intersecting point of Median Upheaval Zone and Fossa Magna. The plain is covered with Molinia japonic and Sasa kurilensis.
