Minerallogically and partly chemically analyzed were three sets of sample taken from the upper half horizons of the Kanto Loam Formation at three different localities in KantO district, that is Mitaka (Tokyo), Utsunomiya (Tochigi), and Akagi (Gumma). 1) To obtain satisfactory result in mechanical analysis and consequently in separation of pure sandy fraction, suitable dispersant was preliminarily sought. Samples containing much allophane clay prefer to acidic reagent, while those containing much hydrated halloysite, to alkaline reagent. 2) Light minerals (sp. gr.<2.85) of fine sand fraction (0.2〜0.02 mm) of each sample were plagioclases, quartz, micas, volcanic glass shards, fragmental volcanic groundmass, plant opals etc. From this, two facts attracted the author's attention. 3) The first fact was that the middle part of the Tachikawa Loam at Mitaka which is the uppermost bed of the KantO Loam Formation contained volcanic glass shards, their index of refraction being too low (n=1.49〜4.50) to be considered of the same origin as the basaltic mother materials. It is assumed that the glass shards may be possibly correlated to those found in Tokai district about 300 km west of Mitaka. However, a short argument was given that the correlation should be carefully carried out before finally concluded. 4) As the second fact, amounts of the plant opals, supposed to be derived from grasses were found in positive relation to carbon contents of the samples, thus being larger in "black bands" or "crack zone" which are high in carbon content and are considered to be buried soils more or less truncated. It may be, therefore, reasonable to suppose that grasses were growing on the ground-surface now buried and made at least some contribution to formation of humus. 5) Through the profiles of the Kanto Loam Formation, several successions of layers could be conceived, each of layers consisting of uppermost darker zone or cracky zone and of lowermost pumiceous or scoriaceous zone with intervening brown "loamy" material. Each layer represent two associated phenomena that in the first phase volcanic ash falls continued without any serious break and in the following quiet phase the fall nearly ceased and weathering as well as soil formation were allowed to take their substantial effects on the just deposited volcanic materials.

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The writer discussed the following problems in this report. 1. From submarine geologic (after NIINO, 1933, 35, HOSHINO, 1958) or tectonic viewpoints, it comes to the conclusion that the shallow bottom of Japan Sea was submarged during the early Miocene. 2. The highland in Japanese Island which have similar scales as the shallow parts of Japan Sea were formed in the latest Pliocene or Pleistocene, and so the shallow parts of Japan Sea were above the sea level at these time. 3. It seems that the sediments having slow elastic velocity (2.0〜2.5 km/sec) and 1.0〜1.5 km thickness on the deep sea bottom (ANDREEVA and UDINTSEV, 1958) were deposited until the latest Pliocene because its velocity is very slow and comparatively constant, and its values are similar to ones of younger Pliocene or Pleistocene sediments in Japanese Island. The above sediments are inferred to be transported through the innumerable submarine canyons from the latest Pliocene to middle Pleistocene. 4. From the above mentioned facts, the deep sea parts are seemed that it was submarged under the sea level in the latest Pliocene or early Pleistocene. 5. Historical review of Japan Sea is shown by Figs.4, 5.

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A number of pyroclastic deposits of the late Pleistocene to Recent are widely developed in the southern part of Hokkaido. Their distribution, source, age of eruption and mode of emplacement have been studied in detail by many geologists and pedologists, resident in Hokkaido. However, mineralogical studies on inorganic colloids of them in the light of modern concepts of clay mineralogy are very scanty. In this paper, based on these geological and volcano-stratigraphical studies, the writers have tried to identify the clay minerals found as alteration products from these pyroclastic deposits, and to consider their processes of alteration from volcanic glasses to crystalline materials. For this purpose, 61 specimens (clay fractions) from eight typelocalities of the pyroclastic deposits were investigated by the use of differential thermal analysis, X-ray powder method, chemical composition, infra-red spectra and electron micrographs. The results are summarized as follows: 1) In the Sapporo-Tomakomai lowland district. In the upper horizon, called Tarumai a and b pumice-fall deposits (less than 300 yrs. B.P.), and volcanic glasses are not altered to allophane. It seems that gel-like substances and nonaltered glass fragments are the dominant components in the clay fraction. In Tarumai c and d pumicefall deposits, "allophane A" described by FIELDES is rich, and downwards in Eniwa a and b horizons (more than 5,000 yrs. B.P.), hydrated halloysite becomes remarkable. In the late Pleistocene deposits, namely in the Shikotsu pumice-flow and Shikotsu pumice-fall (20,000 yrs. B.P.), hydrated halloysite is predominant. 2) In the Tokachi district. The upper horizon is rich in allophane, while downwards, in Tokachi c_2 ash deposit (more than a few thousands years ago), it is characteristic that an irregular mixed layer of hydrated halloysite and halloysite is predominant. 3) In the Nemuro district. There is exceptional irregularity of alteration of allophane to hydrated halloysite. Namely in the upper Mashu f pumice-flow deposit (3,000-5,000 yrs. B.P.), the dominant clay mineral is allophane, that of Mashu k ash deposit is hydrated halloysite, and in the lower Mashu 1 pumice-fall deposit (more than 5,000 yrs. B.P.), allophane is dominant. These facts seem to suggest that an alteration process of allophane to hydrated halloysite is determined not only by the time factor, but is also influenced by the length of the weathering of the deposits and by the size of particles of the parent materials.

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