Red beds are present in the dominantly drab Bima Sandstone at two main localities in northeastern Nigeria. Their lithology and petrography are described and chemical analyses quoted. It is deduced that the climate at the source area was conducive to the production of red soils. Alternating humid and dry periods are believed to have provided the conditions favourable for the accelerated erosion of a provenance of igneous and metamorphic rocks of marked relief. For the most part the pigment appears to have been finely-divided material that was sorted prior to deposition; local environmental conditions determined whether the pigment subsequently remained red or was reduced. The association of oxidising and reducing conditions with shallow-water sedimentary structures may best be explained by the postulation of seasonal flooding of an alluvial plain in a savanna-type environment.