The Myoko volcano, one of the stratovolcanoes in the northern part of the Fossa Magna, Central Japan, has the complicated history (Table 1). The last activity of the Myoko volcano is called the IV stage, and is divided into precaldera, caldera, and central cone substages. The strata formed during this stage are collectively called the Myokosan group which consists of lavas, pyroclastic flow deposits, pyroclastic fall deposits, volcanic mud flow deposits, and lake deposits. They are described in detail and their stratigraphic relations are tabulated in Table 2 and Fig. 4. The rocks of the essential eruptives are basalt, pyroxene andesite and hornblende andesite. They change from basalt to pyroxene andesite and hornblende andesite keeping step with the eruptive order. Quantitatively, the hornblende andesite is predominant.
In 1973, fossil elephant bones were yielded from the sandy formation, at Kamibessho, Sakura-shi, Chiba Prefecture, Kwanto Regeon of Central Japan. The formation, belonging to the lower part of Narita Formation also yielded many other molluscan fossils characterized by Glycymeris yessoensis, Diplodonta usta etc. The molluscan assemblage is closely related to that of Kamiiwahashi fossil beds of Narita Formation in other area except for a few remarkable characteristics, that is; containing less number of the genera than the other Kamiiwahashi beds and being found in thin fossil beds. The fossil materials of the elephant include a lower jaw with the left second molar in situ, and a right tusk separated into three pieces. The mandible is rather large as P. naumanni of M2 stage and the shape of it generally resembles to the holotype of P. naumanni. The features observed on the grinded tooth indicate that the materials belong to the molar of P. naumanni, which is steno-crown type with distinct loxodont plica. The incisor is more thick and stout, suggesting that it belongs to male individual.
For the purpose of testifying a generally accepted hypothesis in Japan, that is, crustal movements have continued in the Quaternary Period with the same mode and the same rate, marine terraces of Okushiri Island, which is located on the west of the Oshima Peninsula, Hokkaido (Fig. 1), were surveyed precisely, because it had been said that the Quaternary crustal movements of this island had changed in a mode by some researchers. The means of this investigation were to classify marine terraces, to measure altitudes of former shorelines of the terraces by an altimeter, and to infer the mode of crustal movements on the distribution of the altitudes obtained. The results are as follows. (1) There are three higher denudation surfaces of marine origin and six marine terraces, the 1st to 6th terraces in descending order (Fig. 3). (2) The altitudes of each former shoreline of the 3rd to 6th terraces are higher in the northwestern part of the island than in the southeast. The general strike of tilting is nearly ENE-WSW (Fig. 4, 5). The inclinations of tilting increase progressively from the younger terrace to the older one (Fig. 6). (3) The equations of interrelation between the altitudes of the 3rd and 4th terraces and those of the 4th and 5th terraces are: T3=1.40T4+1.65 (1) T4=1.04T5+34.4 (2) where T is the altitude of shoreline in meter. (4) Therefore, the hypothsis of“same mode”in crustal movement seems to be accepted in this island, at least since the time of formation of the 3rd terrace. The terraces, however, have been not dated, the hypothesis of“same rate”is not checked. (5) The constants of equation (1) take the same values approximately to those of equations which have been obtained from two terraces in some other part of the Uetsu Fold Zone, a Neogene-Quaternary fold zone, which may be correlated to the 3rd and 4th terraces in Okushiri Island. (6) The mode of tilting inferred from the marine terraces is in accordance with the geologic structure of Neogene sedimentary strata in the northern part of Okushiri. Thus it is probable that such a tilting has continued since Neogene.