The Daisen volcanic ash formation is widely distributed in Tottori Prefecture, Southwest Japan. According to the San-in Quaternary Research Group, this formation is divided into four members ; upper, middle, lower and the lowermost volcanic ash members consisted. The lowermost volcanic ash members of about thirty layers are found at Okachi, Kurayoshi C. Tottori Prefecture. The thirty layers consisted of pumices, loams and pyroclastic flows are divided into eight units, namely, a, b, c, d, e, f, g and h units from the lower to the upper due to the unconformity planes, The eight units are classified into four groups according to the soil colours, namely, the first group (unit a), the second group (units b and c), the third group (units d, e, f, and g) and the fourth group (unit h). We have studied the mineralogical, clay mineralogical and soil micromorphological properties of the above mentioned volcanic ash formations by means of X-ray diffraction analysis, differential thermal analysis, electron-microscopic observations and electronprobe microanalysis. The results of the analyses are summarized in Table 1.

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Pliocene volcanic rocks are widely distributed in the Yoneyama district, Niigata prefecture, central Japan. The volcanic activity is divided into four stages, in each of which volcanic rocks vary from basic to acidic. The volcanic rocks are characterized by porphyritic texture and mainly divided into the following rock types by mineral assemblage of phenocrysts: olivine-augite-basalt with or without hornblende, hypersthene-augite-andesite and hornblende-hypersthene-augite-andesite. The andesites of the Yoneyama district are characterized by the presence of rhombic pyroxene in groundmass. In the basalt, however, groundmass hypersthene is not found. Plagioclase phenocryst attains to 21-35% in modal analyses and usually forms zoned crystals. The composition of plagioclase as phenocryst ranges from 44 to 81% in An content, whereas that as ground-mass constituent from 35 to 65%. The optical properties of mafic minerals are described. One augite and four hornblende phenocrysts are analyzed by the electron microprobe. Thity-one lava, two block in pyrocrastic rocks from the Yoneyama formation, one lava from the Komanoma formation and eight intrusive rocks were chemically analyzed. Chemical composition of the Yoneyama volcanic rocks is characterized by high content of Al2O3, ranging from 17 to 21 wt %, and K2O, 1.2 to 2.7 wt%, and low content of MgO, 1.9 to 5.6 wt%. The potassium Ka X-ray image shows that potassium is concentrated in the interstitial glass and irregular-shaped feldspar of groundmass except lath-shaped plagioclase and granular pyroxene. Normative olivine and nepheline often appear in the basalt. Sr and Rb contents of forty volcanic rocks were determined. Sr and Rb contents are high and their average value is 500 and 74 ppm, respectively. K/Rb ratio is 200 on the average. The chemical composition of the Yoneyama basalt is similar to that of the Pliocene volcanic rocks in the northern part of Nagano Prefecture. The composition of the magma seems to be originally rich in Al2O3 and K2O contents.

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Hiruzenbara is situated at the northern part of Okayama Prefecture and forms the intra-mountaneous basin at a height of about 400 m from the sea level. There develop the river terraces which are underlain by the volcanic products and diatomaceous earthes of non-marine origin. The latter has been called the Hiruzenbara Formation. The writers have carried out the collaborated works since 1971, to clear the geologic age and histories of that formation. Thus, the followings were concluded. (1) The Hiruzenbara Formation is not the Pliocene deposit foremerly considered, but of the middle Pleistocene in age; it may be referred to the M/R interglacial and Riss glacial stages. (2) Diamatoceous earthes of the Hiruzenbara Formation are divided into three diatom assemblages. It shows that the sedimentary environment changed from warm to cool. (3) The Palaeo-Hiruzenbara Lake was filled up and died out in the Riss glacial stage, and subsequently the Hiruzenbara Formation was covered by the volcanic products of Mt. Daisen. Thereafter, four terraces were formed. (4) The Hanazona peat which is intercalated into the lower terrace deposits, shows the age of 21710 Y.B.P. (Gak.-4033). It corresponds to the Maximum Wurm.

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Radiometric ages have been determined over the samples of Apollo 11, 12, 14, 15, 16 and 17 and Luna 16 and 20 rocks and soils. From the agedating data of the lunar materials it is attempted to initiate a framework for lunar chronology. The basalts from mare regions have not undergone shock metamorphism and brecciation caused by the impact events. The ages of mare basalts from Apollo 11, 12, 14, 15, and 17 and Luna 16 date the period of flooding by basaltic lava on mare basins. The highland samples from Apollo 14, 15, 16, and 17 and Luna 20 abound with breccias-rock fragments and soils that have adhered because of the heat and pressure of impacts. Ejecta thrown up by the mare basin impacts formed the highlands. The highland rock samples (anorthositic gabbro composition but breccia texture) give a date for the cataclysm of mare basin excavation and highland formation. The ages for the mare volcanism are: Oceanus Procellarum 3.16-3.36 b.y.; Mare Imbrium 3.28-3.44 b.y.; Mare Fecunditatis 3.4-3.5 b.y.; Mare Tranquillitatis 3.56-3.83 b.y.; Mare Serenitatis 3.71 -3.79 b.y.; pre-Mare Imbrium 3.95-4.0 b.y. For the highland formation: Cayley Plains 〜3.84 b.y.: Fra Mauro Hills 〜3.88 b.y.; Apennine Mountains 〜3.88 b.y.; Apollonius Mountains 〜3.90 b.y. Descartes Mountains 〜3.93 b.y.; Taurus-Littrow Highlands 〜3.98 b.y. For the impact mare basin formation: Orientale Basin 〜3.84 b.y.; Imbrium Basin 〜3.88 b.y.; Crisium Basin 〜3.90 b.y.; Nectaris Basin 〜3.93 b.y.; Serenitatis Basin 〜3.98 b.y. The moon originated about 4.6 b.y. ago. The outermost layers of the moon must have been very hot at that time, by virtus of conservation of accretional energy, as inferred from the wholerock and soil Rb-Sr model ages of 4.6 b.y. Cooling within the outer layers commences after the period of intensive rapid heating. The flooding of the mare basins with basaltic lavas spans a time interval between 3.16 and 4.0 b.y. ago. This shows a second heating of the moon due to long-lived radioactive energy. The highlands are built up by the ejecta from the large (basin) impacts, in especial, from Orientale, Imbrium, Crisium, Nectaris, and Serenitatis events. Ages of highland samples cluster in the interval 3.84 to 4.05 b.y. and indicate that most of the major lunar basins formed in this period by a cataclysmic bombardment of the surface by many large bodies. The failure to discover lunar volcanic rocks which were formed about 4.0 to 4.6 b.y. ago, and younger than those about 3.16 b.y. ago is an important constraint on the lunar thermal history. The moon has been slowly dying since 3.16 b.y. ago, in contrast to the earth, which is, and may be, as active as ever. This results from the fact that the moon is a small body in comparison with the earth. The lunar chronology in this study is consistent with the theoretical thermal calculation (IRIYAMA and SHIMAZU, 1967; REYNOLDS et al., 1972).

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