抄録
(1) Further studies were made on the weathering of pyroxene andesite which was described in the previous report. (2) The results obtained by alkali solution treatments showed that a small amount of alumina (1_??_2%) in the weathering products was existent in the free form. (3) At the early stage, the iron in the rock changes into limonitic oxides and with the progress of weathering the limonitic oxides gradually alter into hematitic oxides. In the weathering products, 81_??_95% of the iron soluble in HC1 are existent_??_r the form of free iron oxide. (4) The formation of weathering complex A2 having the colour reaction of halloysite begins at an earlier stage of the weathering and the complex A2 content becomes maximum either in the yellow or in the grey horizon, and decreases in the soils over the grey horizon. The weathering complex B having the colour reaction of kaolinite is formed at a latter stage of the weathering and gradually increses. It seems that the halloysite formed at an earlier stage in the weathering process is gradully converted into kaolinite. The weathering products contain a small amount of the complex A1 soluble in the acid oxalate solu-tion (pH 4.1). (5) The grey horizon and soils are acid and very poor in exchangeable bases. The exchange acidity is at a maximum in the grey horizon and decreases in the soils. In yellow horizon, grey horizon, and soils, the degrees, of base saturation estimated by the KAPPEN's method were 3.4_??_7.7, and the hydrolytic acidities were 4.5_??_18 times as great as the exchange acidities. (6) The clays (<0. 002mm) separated from the soils contain halloysite, kaolinite, and free iron oxide.
