WEATHERING OF GLACIAL SOIL MATERIAL

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Abstract
The authors have attempted to infer different chemical and mineralogical conditions in the soils of the glacial drifts of n. New Jersey and e. Pennsylvania, by studying alteration products of selected rock specimens of the drifts. Soils of the Wisconsin tills are weathering from comparatively fresh surfaces, and their Illinoian and Kansan counterparts are weathering from materials that have already reached an advanced stage of weathering. A difference in the soil soln. is to be expected if it is in contact with a fresh surface of a mineral compared with a highly weathered mineral. This principle applies throughout the several glacial areas, yet little has been known concerning the actual or relative status of the weathering of the minerals. Partly weathered boulders from the tills were selected, and fusion analyses and petrographic studies were made from fresh cores and weathered rinds of the boulders. A gneiss boulder in Kansan till shows SiO2 of rind to be less than half that of core; Fe2O3 and water of hydration increased greatly in rind; Al2O3 and MnO2 increased slightly in rind; P2O5 decreased slightly; CaO, MgO, Na2O decreased 50%; K2O remained constant. A cobble of basalt in Kansan till shows a silica decrease from 54% in core to 40% in rind; CaO, MgO, Na2O, and K2O decreased 50%; Fe2O3 increased from 12% to 22%; AI2O3 increased 50%; water of hydration increased from 1% in core to 9% in rind; TiO2, P2O5, MnO2 remained constant. A dolomite boulder in Wisconsin till shows an increase of silica from 23% in core to 66% in rind; Fe2O3 increased from 4% to 11%; Al2O3 increased from 1% to 7%. Nearly all Ca and Mg had been leached from rind. Sandstones from 3 drifts, quartzites from Wisconsin and Kansan drifts, and the above mentioned boulders are described petrographically.

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