👉 Underclay is a term used in geology to describe a layer of soil or rock below a bedrock layer. It is typically formed by erosion, weathering, or other processes that cause the underlying material to become less permeable and more susceptible to water infiltration. In general, underclays are characterized by their lack of effective permeability, which allows water to easily infiltrate through them without being absorbed into the soil. This can lead to a number of problems such as flooding, erosion
