Stop 1:  Spring on the Horse Trail.

Get back on Route 100 driving back into town.  Turn Right into the park at the Deep Well Entrance.  Drive through the picnic areas to the parking lot where the road makes a hairpin turn to the right.

Deep Well is at the lowest point in the park.  The rocks and fossils you will find here are the oldest found in the park and date from the middle and late Ordovician Period.  (450-440 million years ago).
 
 
 
 
 
 

Examine the Rocks: Look for rocks starting as soon as you get out of the van. You will find these rocks along the edge of the road on your way to the shelter.  Don't look in the parking area, because that has imported gravel.  You will find two kinds of rocks.  One will be gray and dull.  The other will be brown and shiny (at least when wet).
 

Field Testing and Lab Testing

Field testing is both harder and easier than the testing of rocks that you have done in your classrooms.

It is harder because you don't have as much equipment or as good a place to work. 

It is easier than classroom testing because the range of possibilities is much smaller.  In your classroom exercises, the rock could be anything.  In Nashville, however, we have only five or six common rocks, all of which are sedimentary, and only one of which is hard.  This makes identification very much easier.

Testing hardness:  Instead of a complete Moh's Hardness kit such as you had in your classroom, most geologists I know bring only a knife, which lets them divide specimens into only two hardness categories (relatively hard and relatively soft)

Testing with acid:  Most geologists in Nashville carry a small bottle with a medicine dropper filled with hydrochloric acid (HCl).  To test for limestone, put a drop on the rock.  It will fizz.  You can buy these bottles at any hardware store.  You can buy hydrochloric acid where plumbing supplies are sold.  (It is used to dissolve limestone deposits in pipes).  If you don't want to use hydrochloric acid, you can test with vinegar.  Because it is so much weaker than HCl, putting a drop of vinegar on a rock won't work.  Bring a glass jar partly filled with vinegar, and drop your specimen in it.  Bubbles will rise from the specimen if it contains limestone. 
Do the following tests. If the answers are: you have Limestone (Notice the scar made by the acid in the upper specimen and the scratch made by my knife on the lower specimen.) Limestone is the commonest rock in Nashville.  It is made of the mineral calcium carbonate (as in chalk and Tums antacid).  Limestone forms when shells of organisms (most of them microscopic) fall to the sea floor.  The presence of limestone tells us a great deal about the environment at the time the rock was formed (what geologists call the depositional environment). Under most conditions, these shells simply dissolve, but in sea water which is relatively shallow and warm, they accumulate to form limestone.

You may have read that Nashville was once covered by a warm, shallow sea and wondered "How do they know that?"  Here is the answer. We know that because there is so much limestone found here, and limestone only accumulates under warm shallow seas. Quite a story to be told by such an ugly little rock.
 
 
 
 
 

If the answers are
 

  • No, you can't scratch it with a knife;
  • Yes, it will scratch a knife;
  • No, it doesn't fizz in contact with acid.
    • you have Chert.  Chert is made up of microcrystals of silicon dioxide (as in glass).  This explains why its properties are so different from that of limestone. Chert is formed in two ways.  Nodular chert such as you see here precipitates out of solution like rock candy,

    Walk across the road to the shelter.  Here you will find an excellent map of the park.  Continue through the shelter along the trail to the intersection.  At this intersection turn right along the horse trail which runs parallel to the road.  About fifty paces down the trail you will come to a spring on your left.
     
     

    Examine the spring and draw a sketch of it.   If the spring is flowing, as it does in the spring, the rocks may be slippery.  Keep your eyes open for poison ivy.

    Where does the water appear to be coming from?  How do you think it got there.

    What effect does the spring appear to be having on the hillside.

    What kinds of rocks do you find around the spring?

    Look for fossils.  You will find them.  Don't take them with you (this is a city park), but draw sketches of them so you remember what they look like
     
     
     

    Examine the hillside above the spring.  Draw a profile of the edge of the hill. Notice that the hill does not go up gradually, but has two almost vertical bluffs separated by more gradual slopes.  What do you think has caused that?  Walk down the stream bed to the road.

    Point the compass toward the crest of the hill.  What direction is it?  What side of the hill is the spring on?
     
     
     
     
     
     
     
     
     
     
     

    Examine the stream bed below the spring.
    Look toward the road.  Notice that a small stream has formed below the spring.  What effect is this spring having on the hillside.  Notice that where the stream comes to the road, the park rangers have put in a pipe, to direct it under the road.  Why do you think they did that?


     
     


    When you get down to the road look back up the stream toward the spring.  If you look carefully, you will notice another effect the stream is having on the rocks.  Notice that down by the road, you see mostly pebbles and sand, while farther up the stream you see primarily larger rocks.  The stream appears to be sorting the rocks by size.


     
     
     
     
     
     
     

    Examine the map.

    Walk back on the road to the shelter.  We are about to proceed to Stop 2, but first, we want to look at the map.
     
    Reading a Topographic Map

    A topographic map an attempt to represent three dimensions in a two dimensional chart.  This one is particularly easy to read.  Unfortunately, I have not yet found an equally good one to put on this web site.

    The thin lines represent lines of equal elevation.  This map has lines of equal elevation every 50 feet, with lines every 100 feet labeled.
    Identify the lines of equal elevation.  Look at the roads.  Why do you think the roads follow the lines of equal elevation.

    Our next stop will be at Dripping Spring.  Why, you may ask, do we need to go look at a second spring?  There are things that you can learn by looking at two springs which you cannot know from looking at one.

    Find the spring we have just looked at on the map.  Determine its elevation.

    Next find Dripping Springs and determine its elevation.

    Can you think of a hypothesis to explain why they are at the same elevation?

    Now let's go take a look.
     
     

    Let's go to Stop 2