The rock or deposit from, and on, which a soil has been formed. The nature of the parent rock will largely determine the nature of the regolith, and hence the soil texture—basalt tends to produce clay soils; granite sandy soils. S. Smith (1996) PPG 20, 4 links parent material with bimodality in fluvial beds. See also Mahaney (1993) PPG 19, 3.