Abstract
In this paper the writers describe a new natural accumulation of small scale in the western part of Shizuoka Prefecture. Methane gas occurs in the alluvial deposits which fill the drowned valley of the River Kiku and cover Neogene formations. Through geological and geochemical studies, they come to a conclusion that although the gas was, for the most part, generated in the muddy alluvial deposits and probably the generation is still in progress, it is probable that a part of the gas was derived from the underlying Neogene formations.
