1. Remarkable fossil ripple marks were discovered along the Mamonozawa-gawa of Nakazato-mura, Tano-gun, Gumma Prefecture, in the Cretaceous deposits of the Sanchu Graben. 2. Morphologically most of these belong to the linguoid ripple marks, and some of which are quite characteristic.(PI II) Field observations by the writers as to the Recent ripples formed by the current action, show that these characteristic linguoid ripples are formed only within a depth of several centimeters.(Pl. II) 3. The ripple mark is recognized only on the upper surface of the fine or medium grain:d sandstone stratum, and its surface is covered by a very fine mudstone of dark colour without exception. 4. There are numerous Lebensspuren and two curious holes on the surface of the ripple marks(Pl. I, IV.), and some molluscan fossils which show brackish water deposits are collected on the same horizon with the ripple marks at Sebayashi. 5. Accordingly the writers consider that the sandstone stratum with ripples was formed in the socalled "Wattenschlick" near the estuary, where the depth was only a few centimeters. 6. The horizons of the ripple marks should be divided into two; the lower one belongs to the middle part of the Miyakoan series, and the upper one to the series upper than the Miyakoan.
