Leaching

The wonderful thing about having a little knowledge of science is that you can observe incredible things all around you every day. I  had a quick walk to the shore today, between the showers, and along my favourite trail. This image (with a lens-cap for scale) shows the very definite discoloured soil horizon that occurs when the chemistry of the rain seeping through the soil slowly removes and re-deposits iron-rich compounds at a lower level. Depending on the soil and the duration of the leaching (the slow draining by soil-water) this layer can form a very substantial "iron pan" ie a layer of metal-rich deposits that extends underground just like a metal tray. In some areas, where they want to plant trees for forestry, a special (huge) plough is required to break this iron-pan and turn the soil, otherwise the tree roots find it impossible to break through to the ground beneath, and being shallow-rooted, blow over in the big winds.