Get some bricks (you can use wooden ones). Place some of them in a plastic tray so that they make a square layer. Place four more layers on top. Now pour some water from a jug on to the top layer. What happens to the water - does it seep out of the bottom? Place a washing up sponge on the bricks and do the experiment again. Does the same thing happen? This is a model of soil on rock. Most rocks are cracked and water flows through the cracks, coming out as a spring at the lowest level. Sometimes you can see the rock and sometimes it is covered with a thin layer of soil and grass, just as the pictures showed. Now close this window and look at the pictures again.
