In the reaches of the Salawusu River of northern China, the upper part of thetransitional Salawusu Formation is considered through studies to be the ChengchuanFormation composed mainly of aeolian sands. The Chengchuan Formation and theMalan loess are heteropic deposits (sandy and loessic facies) formed contempora-neously under the wind action. The Chengchuan Formation is quite different fromits underlying Salawusu Formation whether in geochronology, lithology and sedi-meatary facies or in palaeontology. The Chengchuan Formation was deposited inthe Wurm ice age (at about 70 000--10 000 a. B. P.), mainly in an arid, cold,windy and sandy desert and desert-steppe environment;while the Salawusu Forma-tion was formed in the Riss and Wurm inter-ice age, prior to 70 000 a B. P.,mainly in a warm and humid forest and forest steppe environment.