<P> Loess is an aeolian sediment formed by the accumulation of wind - blown silt, typically in the 20--50 micrometer size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate . It is usually homogeneous and highly porous and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs . </P> <P> The word loess, with connotations of origin by wind - deposited accumulation, came into English from German Löss ((lœs)), which can be traced back to Swiss German and is cognate with the English word loose and the German word los . It was first applied to Rhine River valley loess about 1821 . </P> <P> Loess is homogeneous, porous, friable, pale yellow or buff, slightly coherent, typically non-stratified and often calcareous . Loess grains are angular with little polishing or rounding and composed of crystals of quartz, feldspar, mica and other minerals . Loess can be described as a rich, dust - like soil . </P> <P> Loess deposits may become very thick; more than a hundred meters in areas of China and tens of meters in parts of the Midwestern United States . It generally occurs as a blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick . </P>

Where is loess mainly found in the united states