火成岩の風化の関する研究

Abstract

(1) Further studies were made on the volcanogenous soils derived from quartz biotite horn-blende andesitic ejecta in Tottori district. (2) Total analyses showed that the yellow horizons contained considerable amount of alumina, and that the A horizons, as compared with the yellow horizon, had high silica content. The horizons derived from coarse ejecta, namely the B horizon of Tomari-profile and the yellow horizons, had lower values of si, si/al, m/c, alk, and f than the A horizon derived from volcanic ash. The h value was highest in the yellow horizon and somewhat decreased in the A horizon. (3) The yellow horizons contained very large amount of alumina and silica, which were decomposed by HCl, and they were very poor in the portion decomposed by H2SO4 from the insoluble residue in HCl extraction, while in the upper horizons this portion was increased. Ca and Mg were contained in the hornblende remaining in fresh state, as in the soils from biotite hornblende anctesite previously reported. (4) In the volcanogenous soils studied, from 86.7 to 99.8% of the iron oxide soluble in HCl was made up of free iron oxide which was limonitic in the yellow horizon, and which consisted of limonitic and hematitic oxide in the upper horizon. (5) In the yellow horizons containing very little humus, the exchange acidity was very low (y1:0.00 and 1.05), but the hydroytic acidity was very high(y1:74.0 and 122.8). It seemed that this great predominance of hydrolytic acidity over the exchange acidity was originated in the nature of allophane-like substance. The exchange acidity increased in the A horizon (rich in humus).