What is the term for soil that is formed in place from the underlying parent materials?

• A. Transported soil
• B. Organic soil
• C. Residual soil
• D. Alluvial soil

Answer: (C)

Residual soil is formed in place from the weathering of the underlying parent materials, meaning it develops directly from the rock or sediment that is in situ rather than being transported from another location. This process involves the breakdown of the parent material through physical, chemical, and biological processes over time. As weathering occurs, new soil horizons are created from the materials derived from the bedrock or parent material, leading to a unique soil composition that reflects the characteristics of the local geology.

Transported soil, on the other hand, has been moved from its original location by natural forces like water, wind, or glaciers. Organic soil primarily consists of decaying plant and animal matter and does not describe the formation process from rocks or sediments. Alluvial soil is a type of transported soil specifically found in floodplains and riverbeds, formed from sediment deposited by running water.

Understanding these distinctions helps clarify why residual soil is the correct term for soil that evolves directly from the underlying materials without being relocated.