Site 5: The Stadium

Boy howdy, there is a lot to talk about here, two laws of geology, a principle, and joint caves, all set against the lovely backdrop of a waterfall and cliff.


First lets discuss the Law of Superposition. This law states that the oldest rock layer will be found on the bottom of a rock outcrop. That makes sense, have you even gone to a fair or carnival and made the different colored sand in the jar? Where is the sand you put in first? On the bottom! Looking at the large rock outcrop across the stream, the oldest layer is on the bottom and the youngest is on the top, this is a time span of millions of years of history.


Next we should talk about the Principle of Uniformity, which states that things happened in the past, the same way things happen today. The example we see at this site is ripple marks preserved in the rock. Here we see an example of sand ripples made in shallow tidal water at a beach. Yes, but what does it all mean? It means that geologists can infer the the environment in which some of the rock from this outcrop formed was tidal because it has ripples preserved in the rock.



Lets pause for a minute from all these laws and principles to talk about joint caves. There are some delightful examples of joint caves at this location. Joint caves form when surface water soaks through the soil to the bedrock, then travels down through a joint crack until it reaches the bottom of the crack. At the bottom of the crack, the mildly acidic water begins to chemically weather the limestone. Over time the opening becomes larger and larger. If you look carefully at this picture you will see a vertical crack directly above the cave, that is the joint crack.










The last item to discuss at this station is the Law of Original Horizontality. This law states that sedimentary rock layers are all formed horizontally. When you see something different in a sedimentary rock (ie it is bent or folded) then there were tectonics forces at work on it.




Before we split, lets check out out escape route... straight up the joint crack.