in some exceptionally ancient soils

Scanning electron microscopy (SEM) was used to study the effect of prolonged weathering on the micromorphology of quartz sand. Three soil chronosequences in the southeastern United States (Virginia), with weathering profiles ranging in age from ~ 90 ka to ~ 10 Ma, were studied. Detrital sand grains from soil B horizons show that dissolution features are crystallographically controlled and develop progressively over time from smaller to larger etch pits, then to an intercon-nected network of grooves and crevasses, and finally to bulk grain decomposition. SEM also shows that disintegrating quartzite clasts in the oldest gravelly soils have been preferentially leached of silica cement, possibly due to selective weathering along 'dust lines ' and spalling-off of quartz overgrowths. Severely etched quartz, usually attributed to tropical weathering, is an unreliable paleoclimate indicator because similar features can form as a result of prolonged weathering under a temperate climate. However, the well-defined relationship between quartz micromorphology and duration of weathering suggests that SEM is a useful tool for soil correlation and geomorphic analysis. 1