ity: visible; position: absolute; top: 507px; left: 380px; width: 325px; height: 51px } #layer53 { visibility: visible; position: absolute; top: 39px; left: 370px; width: 325px; height: 35px } #layer55 { visibility: visible; position: absolute; top: 24px; left: 218px; width: 145px; height: 207px }-->

This diagram shows what happens to some rocks when water flows through them. The water changes colour and the chalk disappears. In rocks where this happens, the holes quickly get bigger, so even more water can flow through them.