Layers in the soil develop because of the additions, losses, translocations, and transformations that take place as the soil ages. The soil layers occur as a result of water percolating through the soil and leaching substances downward. The layers are parallel to the soil surface and are called horizons. Horizons will vary from the surface to the subsoil and from one soil to the next because of the different intensities of the above processes. Soils are classified into different groups based on the characteristics of the horizons.