Black humic soils with a popular name "Kuroboku soils" mark a characteristic soil group in Japan, although their taxonomical situation has not yet been established, despite of numerous publications of studies. They lie on both of volcanogeneous or non-volcanogeneous parent rocks, especially exhibiting a marked black hue upon volcanogeneous materials. Until recently, a top soil horizon has been assigned to an A horizon, based upon the assumption that the soils may have resulted through transformation of the top of the parent materials, in the process of soil formation, which differing from normal geological process of deposition. I have long conceived that the constituent material of the "Kuroboku soils" may have been accumulated through wind transportation and mass-wasting roughly since the beginning of the Holocene period. The "humic volcanic ash soil" upon the Pleistocene tephra layer, which is the most common type of the black soils in Japan implies that volcanic ash showering at times fell out through the process of concentration of humus. Even in the case of non-volcanic humic soils, the formation may primarily be due to the accumulation of atmospheric dust from various sources along with the mass-wastes from nearby slopes. Many instances based on sedimentological, archaeological and mineralogical considerations seem to demonstrate that this top soil horizon is by no means the A horizon of the soil profile, but may essentially be a stratigraphic unit having been accumulated through settling of both organic and inorganic materials supplied onto from nearby and remote environments.

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The volcanic ash soils in Miura Peninsula were found to have some peculiar characteristics. Differing from the other volcanic ash soils in southern Kanto, these soils contained distinct amount of halloysite and 14Å minerals in clay fraction. The materials of these soils were composed of three sheets of volcanic ash falls, that was, soft brownish black humic loam(I), soft reddish brown loam(II) and compact yellowish brown loam(III). In the case of tephra III, platy volcanic glasses were very rich. On the other hand, in the case of tephra I and II, the contents of volcanic glasses were remarkably low. These sequence of tephras are widely distributed in southern Kanto, but in the other region, these are covered with more fresh volcanic ash showers. So it may be said that the volcanic ash soils in Miura Peninsula have been developed from comparatively older ash loam, in which the contents of easily weatherable volcanic glasses are low. In the soils on the undulating topography of Miura Peninsula, weathering proceeds more gently and 14Å minerals such as vermiculite are formed from crystalline primary minerals. The soils on the flat parts are weathered more strongly under well drained conditions and in such soils, hydrated halloysite is observed in the upper horizons and Al-chlorite in the lower horizons. From the peculiarities above mentioned, the volcanic ash soils in Miura Peninsula must be classified as a special genus of Humic allophane soils.

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It has been considered by many workers that the essential clay mineral is allophane in the early stage of weathering of volcanic ash soils and the most probable weathering sequence of those soils in Japan has a following process : volcanic ash→allophane→halloysite→metahalloysite. However, it has been revealed that the essential crystalline clay mineral of volcanic ash soils in the Tohoku and Hokkaido districts of Japan is 14Å clay mineral. In the early stage of weathering the 14Å clay mineral is montmorillonite, and is transformed to vermiculite with aluminum in the interlayer position. Aluminum is more intensely fixed in the interlayer position of the clays in the A horizon than in the lower. From these results the dominating weathering sequence in volcanic ash soils in the Tohoku and Hokkaido districts of Japan is considered to be as follows : volcanic ash→amorphous materials→montmorillonite→intergrade of vermiculite and Al・chlorite. A 7Å kaolin mineral of which (001) spacing is about 7.15 to 7.25Å, is also included in a small amount, and is assumed to be poorly crystallized kaolinite. This mineral seems to more or less increase as weathering proceeds. Halloysite which has never been found in the A, B and C horizons in the volcanic ash soils, is only included in the deeper horizon from the surface. The genetical relationship between halloysite and a 7Å kaolin mineral is indistinct at present.

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The accumulation of organic matter in volcanic ash soils has been discussed on the basis of a simple mathematical model; dX/dt=A-rX (1), where X is the organic matter in the soil, A the annual addition of plant residue, r the fraction of X decomposed of the soil organic matter per year and t time. By integrating the equation (1) on the assumption of the constancy of A and r, and substituting X by C, the following equation is derived; C=C_m-C_me^<-rt> (2), where C is the carbon % of the soil (corresponding to 10 cm depth of the original ash) and C_m the maximum carbon % of the soil at an equilibrium; dX/dt=0=A-rX. The values of A (=2.1-4.4 ton/ha), r (=0.005-0.0105) and C_m (=20%) are at first estimated from available data on the soils at the supposed equilibrium, and the curves representing the most rapid and slowest accumulation of the organic matter expecting in the volcanic ash soils are depicted in Fig. 1. No suitable datum has been availble to test the feasibility of these accumulation curves except for those in the very early period, which show a reasonable agreement. Then, the value of r has been checked by comparing the average age of the organic matter calculated on the basis of the above accumulation model with that estimated from the measurement of its C-14 specific radioactivity. The average age of the organic matter t^^- at some time t is t^^-=(_0∫^tt(C_m-C_me^<-r>) e^<-rt>・dt)/(_0∫^t(Cm_-C_me^<-r>) e^<-rt>・dt) (3), where (C_m-C_me^<-r>) is the annual increment of the soil organic carbon. By integration, the t^^--t relationship is calculated from the following eaqution ; t^^-=1/r((e^<-rt>(-rt-1)+1)/(-e^<-rt>+1)) (4) The t^^--t curve with r=0.005 (Fig. 2) that corresponds to the slowest accmulation in Fig. 1 shows the maximum average age of the organic matter to be 200 years. The available data of the C-14 age of surface volcanic ash soils, however, indicate much greater average age, and hence much smaller r values such as 0.000125 to 0.0005. This disagreement between the values of r calculated and observed has been solved formally by introducing a factor f, the fraction of A entered into the reservoir of the soil organic matter, into the equation (1). Then, the most probable C-t relationships expecting in the accumlation of the organic matter in the volcanic ash soils are calculated using the equation (2) and delineated in Fig. 3 with hatched lines, where the initial rapid accumulation has been also taken into consideration. The C-t (Fig. 3) and the corresponding t^^--t (Fig. 2) curves thus derived can be used for the dating of the deposition of a buried volcanic ash. As an example, analyses of the data related to the deposition of particular ashes " Imogo" in Kyushu Island have been attempted. The probable time limits for the initiation and termination of the organic matter accumulation (as shown in Fig. 4 as white and black rectangles, respectively) are calculated from the C-14 age of the soil organic matter (vertical arrows) which accumulated in the volcanic ash layers deposited below and above "Imogo" ashes. Comparisons of these time limits have led to conlcude that there are at least two different "Imogo" ashes; the one deposited at 5000〜5250±300 yr. B.P. (lateral arrows) and another deposited not earlier than about 4000 yr. B.P.

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Volcanic ash soils in this prefecture are mainly distributed on terraces of 20〜40 meters above the sea level, and have 2〜4 meter's thickness. These soils, can be classified 5 types as follows: The black volcanic ash soil, the dark brown volcanic ash soil, the brown volcanic ash soil, the wet volcanic ash soil and the reworked volcanic ash soil. Among these soils, the productivity of the reworked volcanic ash soil is the highest, and that of the wet volcanic ash soil is the lowest. The soil productivity depends mainly on calcium and available phosphorus contents in soils. In order to obtain the stable crop yield, it is necessary to keep, 40% of calcium saturation and 5 mg of available phosphorus (P_2O_5) contents in soils.

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Humus composition of two iron-humus podzols and one iron podzol in the British Isles was determined by the method proposed by the author, and the results were compared with those of mountain podzols in Central Japan. The results may be summarized as follows: 1. A large part of humus was extracted with sodium hydroxide, and the amount of humus extracted with sodium pyrophosphate from alkali-treated soil was very small. 2. In iron-humus podzols, not only L, F, H and A_1 but also A_2 and B_1 (humus accumulation) horizons contained more humic acid comparing to fulvic acid, and the reverse was the case in B_2 and underlying horizons. On the other hand, in iron-podzol, similar to mountain podzols in Japan, the amount of fulvic acid exceeded that of humic acid in A_2 and successive deeper horizons. 3. The greater part of humic acids showed the absorption spectra indicating the presence of so-called green humic acid (Pg). It was considered however, that the content of Pg in these humic acids was not so high as that in Japanese mountain podzols, and the degree of humification was generally higher in humic acids of English podzols than in those of Japanese mountain podzols. 4. A type humic acid having a high degree of humification was recognized in H and A_1 horizons of iron podzol. It was presumed that the fact might be related to the charred wood abundantly found in these horizons.

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A dark montmorillonitic soil on Tertiary mudstone was found at a foot of hilly land of Yui, Shizuoka Prefecture (35°N, 138°E), near the Pacific coast of central Japan. Profile characteristics of the soil are as follows. Soil horizon sequence is A/C; soil texture is heavy clay; soil colour is black grey with a chroma lower than 1.5; mottles are common below the depth of 40cm; when it is dry, the surface horizon has a well developed fine angular blocky structure and in the lower horizons development of cracks causes coarse blocky structure, whereas, when wet, soil consistence is plastic through the whole profile. Chemical features are noted regards total carbon content being lower than expected by the blackish colour of the soil, very low phosphorous absorption coefficient, slightly acidic reaction, high value of CEC, high degree of cationic saturation, and predominance of exchangeable calcium. All the above descrption suggests the soil is akin to Grumusol, Regur, or Typic grumaquert of the 7th Approximation of USDA, except a slight acidity and the absence of free carbonate, probably due to moderately heavy annual precipitation (2400mm), and except a larger amount of humus possibly resulted from the grass vegetation and the poor inner drainage of the profile. In conclusion, the soil could be correlated to a member of the Grumusol or the one being alike, having some degree of tendency toward Humic gley soil or Pseudogley soil. Especially favorable conditions must have been continued to form the Grumusol like soil in central Japan. Thus, the soil inherited abundant montmorillonite clay from the parent mudstone. At a lower part of hill-slope, in wet seasons, seepage water must not only have maintained the clay under expanding state which inhibited inner drainage and leaching of bases, but also have supplied sufficient bases to the solum. The resultant plenty of bases might be enough to make the montmorillonite clay stable in the soil profile.

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Specimens of soil clays derived from the serpentinite in northern Hokkaido have been examined by electron micrographs and electron diffraction in a study of the identification of the serpentine minerals. The results of the investigation showed that the serpentine minerals in the soil clays were composed of antigorite, lizardite and chrysotile. The clay mireralogical properties of these minerals were summarized as follows: 1) Antigorite. Electron micrographs (Figs. 2-1 and 2-3) show thin plates with approximately rectangular outlines. Electron diffraction patterns from single crystals are of the type shown in Figs. 2-2 and 2-4. Layer lines are evident corresponding to a parameter b=9.40Å parallel to the longer morphological axis. Along each layer line, mainly grouped around reciprocal lattice points of a simple 5.6Å×9.4Å rectangular net, are clusters of spots closely spaced at regular intervals corresponding to a cell parameter of approximately 40Å. The pattern may be regarded as similar to those from plates of lizardite on which a superlattice periodicity along the a axis has been superimposed. 2) Lizardite. Electron micrographs (Fig. 3-1) show the irregular plate-like morphology of the fine particles. The pattern obtained from a single crystal of lizardite (Fig. 3-2), is a hexagonal array of spots corresponding to a centered rectangular net of dimensions a=5.25Å, b=9.25Å in agreement with the x-ray powder pattern which gives a=5.31Å, b=9.20Å (WHITTAKER and ZUSSMAN, 1956). 3) Chrysotile. Electron micrographs (Fig. 3-3) show elongated smooth-edged fibres frequently with a thin white axial line. One fibre and its electron diffraction pattern are shown in Fig. 3-4. The diffraction patterns resembled closely those obtained by x-rays with the beam normal to a fibre. Reflections are distributed along "layer lines", the spacing of which corresponds to the repeat distance a=5.38Å along the fibre axis.

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