Of the many types of inter-formational disturbances, the mudflow type is discussed here., The major area in which investigation was undertaken is the vicinity of southern Kanto, and various parts of Japan are also considered., The following are summarized as the conclusion: 1) The mudflows are the products of intense crustal movements, which are supposed to be more frequent in the earliest and the latest stages of the development of a single group consisting of sedimentary formations., 2) The characteristic feature of these mudflows is the contamination of coarse sediments into finer fractions., 3) The mudflows are variously modified by certain geological features: e., g., tectonic framework, sedimentary environments etc., The angle of the slope to initiate the mudflows might be in the range of 3 to 10 degrees., 4) The condition necessary to stabilize the sediments after the mudflows is the existence of a flowing water mass succeeded by a stagnant condition.,