Engineering geology
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Parent Material

The source of the weathered mineral matter from which soils develop is called the parent material and is a major factor influencing newly forming soil.

Gradually this weathered matter undergoes physical and chemical changes as soil formation progresses. Parent material can either be the underlying bedrock or a layer of unconsolidated deposits. When the P-material is the bedrock, the soils are termed residual soils; while soils developed on unconsolidated sediment are called transported soils. It should be pointed out that transported soils form in place on parent materials that have been carried from elsewhere and deposited by gravity, water, wind, or ice.

Parent material influences soils in two ways. First, the type of P-material influences the rate of weathering and thus the rate of soil formation. Also, because unconsolidated deposits are already partly weathered; soil development on such material will likely progress more rapidly than when bedrock is the parent material.
Second, the chemical makeup of the P-material will affect the soil’s fertility. This influences the character of the natural vegetation the soil can support. At one time, the P-material was thought to be the primary factor causing differences among soils.

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