Abstract
AbstractSamples were taken of soils formed on volcanic materials varying in age from Cretaceous to Recent. The soil samples were analyzed for particle size distribution, pH, organic matter, cation exchange capacity, and exchangeable cations. Clays were separated and identified by X‐ray diffraction supported by chemical analysis. Clay mineralogy varied with age of the parent material. Recent ash in western Montana from sources in Washington and Oregon gave rise to amorphous clays in eight of nine samples. Soils on Quaternary volcanics near Yellowstone National Park had amorphous or poorly crystalline 2:1 clays. Clays of soils from Tertiary age volcanics were dominated by smectite. Cretaceous volcanics gave rise to mixed 2:1 clays similar to soils on Cretaceous sediments in the Northern Great Plains. Exchangeable cations in the soils varied with the dominant clay minerals.
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