Colluvium specific geological setting. Alluvium is sand, clay, or other similar detrital material deposited by running water. The distinction between colluvium and alluvium relates to the involvement of running water. Alluvium specifically refers to the geomorphic processes involved with flowing water and so alluvium is generally fine-grained clay and silt material that has the capacity to be entrained in water currents and eventually deposited. For these same reasons, alluvium is also generally well sorted material while colluvium is not. Colluvium Colluvium (also colluvial material or colluvial soil) is a general name for loose, unconsolidated sediments that have been deposited at the
Parent rock Parent rock Parent rock, also referred to as substratum, refers to the original rock from which something else was formed. It is mainly used in the context of soil formation where the parent rock (or parent material) normally has a large influence on the nature of the resulting soil. For example,clay soil is derived from shale while sandy soil comes from the weathering of sandstones. The term is also used in the context of metamorphic rocks where again the parent rock or protolith refers to the original rock before metamorphism takes place. Parent rocks can be sedimentary, igneous or metamorphic.