 Saprolites form in the lower zones of soil horizons and represent deep weathering of the bedrock surface.In lateritic regoliths – regoliths are the loose layer of rocks that rest on the bedrock – saprolite may be overlain by upper horizons of residual laterite; most of the original profile is preserved by residual soils or transported overburden.Weathering formed thin kaolinitic [Al2Si2O5(OH)4] saprolites 1,000 to 500 million years ago; thick kaolinitic saprolites 200 to 66 million years ago; and medium-thick immature saprolites 5 million years ago in Sweden.