Loess

Loess, a loose, fine-grained rock, generally pale-coloured, composed of clay, sand, and occasionally lime, and containing a few land-shells and plant remains, but neither sea-shell nor pebble. It occurs over wide areas, especially on continents, independent of existing river-valleys, and is occasionally converted by a copious admixture of humus into rich "black lands," as in Siberia and Western Canada. The prairies between the Rocky and the Alleghany ranges seem to be composed of it, as are also perhaps the "pusstas" of Hungary and an immense area in China. The river Hoang-ho cuts terraced valleys in it to a depth of 1,000 feet, the sides of these valleys having been excavated into underground villages by a teeming population to avoid the extremes of heat and cold. The river gets its name (hoang meaning "yellow") from the abundance of fine sediment suspended in its waters, as does also the Yellow Sea (Hoang-hae), which receives this sediment. Loess would seem to be, at least mainly, accumulated by wind action.