Quaternary fluvial deposits of the rivers Weser and Leine contain abundant heavy minerals of volcanic origin (mainly Augites and Oxyhornblende). The amount of these minerals decreases from South to North and mostly, with growing age of the sediments. The volcanic minerals have been traced back to the oldest Quaternary. Probably the sources of the volcanic minerals are enormous tuff eruptions In the Eifel region during the early Quaternary, perhaps supplemented by volcanic ashes from other areas. Since that time the heavy minerals of volcanic origin must have been present in great quantities within the soils, ready for erosion by the rivers.