Abstract
The writer discussed the geological meaning of the "Fossa Magna" in the ght of recent data, accumulated by various members since the Second World War. He concluded that the usual definition of the "Fossa Magna" included two __efferent technic features. Namely, one of them is a product of the geological history until the close of the Palaeogene, and the other is concerned with the green tuff volcanism and its subsequent diastrophism. Considering the palaeogeographical maps in various periods, he assumed that the syntaxis of the " Fossa Magna " was commenced during the early Jurassic at the latest. The former is bordered by "Itoigawashunto tectonic line" in the west, and by "Katashinagawa tectonic line" (partialy coinciding with Tonegawa line) in the east. T e writer proposed that the word of "Fossa magna" ought to be restricted to this feature. The latter has been made by the fault happened at the earliest time of the Neogene along a line connecting Shizuoka, Okaya, Tokamachi and Shibata city. It is accompanied by violent volcanism and subsequent depression along it. Their tectonic history is corresponding to the orogenesis of the Green tuff region in Japan.
