The Pliocene marine sediments exposed on the dipside route along the River Koito demonstrate a remarkable change in rock facies towards the west., To cleariby the chronological interrelation of the various rock facies, the many pyroclastic key beds were traced in the field., Thereby the interrelation of the extension of each rock facies in time and space was confirmed., The basal characters of the Ichijiku sand facies and the Higashihigasa sand and gravel facies are not unconformable as previously thought, but these coarse sediments merge rapidly and laterally into fine-grained sediments (Figs., 2∼6)., New time and rock-time units are introduced based upon two adequately selected key layers which are considered to be of simultaneous deposition.,