The lowermost loess, the Crowley's Ridge Loess, accumulated during the late Illinoian Stage. The middle loess, Sicily Island Loess, accumulated during early Wisconsin Stage. The neotropical loess is made of silt or silty clay. Soils underlain by loess tend to be excessively drained. The Yellow River in China carries yellow sediment from eroding loess soils. Eroded loess silt gives the Yellow River its color and name. The sediment originates primarily from water erosion in the Loess Plateau region of the northwest. There are layers of flood-deposited loess and loam of Pleistocene origin running through them. The landscape is characterised by large Loess and Marl deposits. The soils developed on loess are generally highly productive for agriculture. It is a typical mountain plateau widely covered by loess. Braunerden are widespread and frequently occur on unconsolidated parent sand or loess parent materials. Other researchers stress the importance of volcanic material in the neotropical loess.