Thursday, September 25, 2008
Springs form when water seeps through the overlying layer of sandstone (Slick Rock). Sandstone is a permeable layer of rock meaning that water can flow throughout the rock. When the water reaches a layer of shale which is non-permeable,meaning that water cannot pass through (Dewey Bridge), it follows the contact between the two layers until it escapes. While the water flows between the contacts, it is eroding the rock that it flows through. As the water flows along the contact between the Slick Rock and the Dewey bridge, the Dewey Bridge is eroded. This leaves the Slick Rock with no support underlying it. The result of this is the slick rock collapsing. Small cave-like structures are formed, much like that in the picture. Water continues to flow through the sandstone and along the contact between the two layers. As a result of the water and the loose sediment, vegetation is able to grow.