Get back in your car and proceed around the hairpin turn to the right.  Follow the road slowly for 1.3 miles, until you come to the first intersection (a road comes in from the left.)  Pull off the road at this intersection and park.  Walk back down the road from which you came.  In about 50 feet you will see a trail cross the road.  Head left on the trail (down the hill).

Examine the small bluff by the trail:  At first the trail goes down hill quickly, then is levels out.  Soon after that, you will see a small bluff on the left side of the trail.

• Is this rock similar to the rock we found near the first spring?

• Test a piece of the rock with your knife and acid.

• What part of the exposure at Site 1 looks most like this one.  Why do you think it is eroding more slowly than the other rock?

Examine the Chattanooga Shale:  Just beyond the rock face, you will see a fallen tree on the left.  Above the rock face beside this tree you will find rocks very different from the ones you saw at the first spring.  This is the Chattanooga Shale.


Describe this rock.  How does it differ from the limestone and chert you found at Stop One? How hard is it? Is it easy to break?  Does it fizz in contact with acid?

If you look carefully, you will find pieces of Chattanooga shale both above and below the bluff.  Do you think that the stratum Chattanooga Shale is above the bluff or below it?

Why do you think this rock is so very different from the limestone that we saw by the first spring and on the bluff?

Different depositional environments create different rocks.  Shale is made when clay settles out of water.  The water was very much muddier when the Chattanooga Shale was deposited than when the Ordovician limestone was deposited.

Until recently it had been believed that the Chattanooga Shale had been deposited in deep water with very little oxygen in it (anoxic).  Recently, however, new discoveries have indicated that the situation may have been more complicated that that.  For an introduction to the Chattanooga Shale link here and scroll down to section on the Chattanooga Shale. For information on the new analysis of the deposition of the shale, link here.

Scientists believe that the Chattanooga Shale was deposited about 360 million years ago.

How do we know that?

The Chattanooga Shale contains Uranium, so, unlike most sedimentary rocks, it can be dated  by radiometric dating.  It was formed 360 million years ago.  The Ordovician Period ended 440 million years ago.

So where are all the rocks from the years between 440 million and 360 million years ago?

Sedimentary rocks are only deposited when the area is accumulating sediment, either under water or in a relatively low place such as a lake or river bed.  Between 440 and 360 mya, Nashville was out of the water.

Gaps in the geologic record like this one are very common.  They are called unconformities.

Examine Dripping Springs:

Continue along the trail until you come to Dripping Springs.  You can tell you have arrived because it is marked by a sign.
 
 
 
 
 
 
 
 

Before you take the detour, go take a look at the spring itself.

How does it compare with the first one we saw?

What rocks do you find at the spring?  Ordovician Limestone?  Chattanooga Shale?

Look for fossils?  (Sometimes I find them, sometimes I don't)
 

 

Now go down below the spring on the detour and see what the water from a little spring, which runs only six months a year can accomplish.










You can now return to your car.  Do you notice how much harder it is climbing up the trail is from going down?  Why do you think this is?

The same gravity which works to erode mountains also works on you.
 
 



Go to Stop 3