Sand, silt, clay and soil loss

If you dig deep, soil changes. At the very top there may be dead leaves, then the dark topsoil that is full of humus, roots and living things. Below it is the subsoil, which is lighter in colour and has less humus. At the bottom is the bedrock, solid rock from which soil forms. Soil and climate affect each other. In a very wet climate rain washes nutrients down through the soil. In a hot, dry climate soil is dry and poor in humus. Sandy soil in a dry grassland drains quickly and holds little water. Grasses cope with it better than big trees, so grass-eating animals live there, followed by fast hunters. Wet clay soil holds water, so plants of wet places grow well. In Egypt the dark silt of the Nile valley is fertile, so crops grow well there.