Abstract

In Madagascar, stonelines (horizons of quartz pebbles in laterites) are buried colluvial and alluvial lag gravels that outline former hill and valley surfaces. Their fabrics, especially rare multiple stone layers, identify the stonelines as old surface lags, and the immature geochemical compositions of their over-burdens relative to their substrates demonstrate burial by colluvium. Hill-mantling stonelines are convex upward and less well developed, whereas those lining valleys are concave to irregular, thicker, deeper, better packed and sorted, and have more rounded stones. Local differences in position between former and modern landforms demonstrate that, in a complexly and tightly folded metamorphic terrain, hills and valleys are likely to shift as the landscape is lowered by weathering, thus implying that the landscape is held at a relatively submature stage of development.

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