Some loess is produced directly by glacial action in a two-stage process. Sand-sized quartz is first formed and then these grains are crushed. Quartz grains of about 80 mu are most easily raised and carried by the wind. Characteristic vertical structures of loess deposits are due largely to the cohesive nature of the material and are interpreted as due to the fact that the interparticle Van der Waals forces are of the same order of magnitude as the weight of the particles. Six events are distinguished in the history of formation of loess--formation and crushing of the material by glacial action, transport of the detrital material by glaciers, deposition from meltwaters, eolian transport, and a second depositional event.

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