mineral soil

Soil composed primarily of weathered rock particles — sand, silt, and clay — as opposed to the organic layers (litter, duff, humus) that sit on top of it. Mineral soil is what you reach when you scrape away the forest floor. In firefighting, a handline scratched down to mineral soil removes the organic fuel and creates a bare surface the fire cannot cross. In ecology, mineral soil is the basement — the foundation on which the organic world builds.