ROCK WEATHERING AND SOIL FORMATION ON HIGH‐ALTITUDE PLATEAUX OF MALAWI

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Abstract
Summary: Humic ferrallitic soils occur at altitudes above 6,000 ft on syenite plateaux. The top‐soil organic‐matter content, 5–10 per cent, exceeds that of all other Malawi latosols. The organic‐matter content of Malawi soils increases rapidly between altitudes of 5,000 and 5,600 ft, corresponding to a fall in mean annual temperature from 65° F to 63° F. The humic top‐soil overlies a yellowish‐red, friable sandy clay or clay with a weak blocky structure. Soils less than 3 ft thick overlie up to 10 ft of weathered rock containing core‐stones. Studies of materials from Zomba Mountain show that, in the formation of weathered rock, the dominant process was bauxitization, with considerable differential removal of silica; gibbsite was derived directly from feldspar. The gravelly bauxitic layer is the parent material for soil formation, in which kaolinization is the dominant weathering process.