How to Read the Rocks Around Our Pond

The rocks around our pond have stories to tell if you know how to listen.  Thanks to Mr. Smail, our high school Geology teacher, for showing me how to read our rocks.  Here are a few of the amazing things I learned from him about the flat rocks that border the pond:

Rock # 6, my favorite.

ROCK FORMATION:

Our rocks are ANCIENT.  Middle Tennessee rocks were mostly formed 300-500 million years ago, during what is called the Paleozoic Era.  During that time, life was growing mostly in the oceans and just beginning to expand to land.  The area that would one day be called Tennessee was covered with a shallow ocean at the beginning of the Paleozoic Era.  Many ocean organisms in the Paleozoic Era produced hard shells made of calcium carbonate.  When those organisms died, their shells accumulated, compacted, weathered and eventually formed limestone, which is the type of rock we have in our outdoor classroom.  Many of today's ocean organisms also have calcium carbonate shells, so they are just starting to form limestone of the distant future.

Here's a map to the rocks around our pond.  The map has numbers so you can find the things I'll talk about here.  Feel free to print the map and draw or write your observations on it.

Map of rocks with numbers (zoom in to see numbers).

Many areas of our rocks are smooth limestone, like almost all of rock 19.  The smooth limestone was produced when the water above the forming rocks was calm.  The calm water washed tiny, tiny bits of shell onto the ocean floor that built up and solidified into smooth limestone.  Before the tiny bits turned into stone, they would have felt like smooth mud.  On several rocks, it appears the mud dried and cracked before turning to stone.

Rock 13 with smooth rock made from dry, cracked smooth mud.

Some areas of the rocks have larger particles and lots of fossils (see below).  These formed when the water was more turbulent and washed larger particles onto the ocean floor.  Rocks 1 and 2 are mostly made of larger particles.  If you've walked on a beach made of very rough sand, you know what sizes of particles formed this rough limestone.

Most of our rocks are made of the rough limestone mostly covered in a smooth layer of limestone.  Rocks 15 and 16 are different.  They were likely made when very turbulent water mixed big pieces of smooth limestone with large shell bits that cemented into rough limestone around the smooth limestone bits.

FOSSILS:

The signs of ancient organisms in rocks are called fossils.  Since limestone is made from the shells of ancient organisms, you can expect to find LOTS of recognizable fossils in our rocks.  The most common fossils in our rocks are shells of ancient clam-type organisms.  We have a few whole shells (Rock #2) and lots of c- or j-shaped fragments or pieces of shells (most rocks).  We also have fossils of long, segmented organisms called nautiloids.  Nautiloids were relatives of modern-day squids, and like squids, they were predators that chased down their prey.  There are always fewer predators than prey in an ecosystem, so it makes sense that there would be fewer nautiloids than clam-type shells.  Rocks number 6 and 17 have nautiloid fossils.

C- and J-shaped shell fossils in Rock #6.

Gorgeous nautiloid fossil in Rock 6, surrounded by shell fossils.

The fossils above are body fossils, or actual fossilized body parts of ancient organisms.  Another type of fossils, trace fossils, are fossilized evidence that organisms were present, like footprints or trails.  The light squiggly lines in many of the smooth limestone areas are trace fossils of burrows or trails left by soft-bodied organisms like worms.  Soft body tissues cannot form fossils, but we can learn a bit from trace fossils about ancient soft organisms.

Lighter squiggles are trace fossils, evidence that soft organisms were once present here.

NOTE TO TEACHERS:
Mr. Smail would be happy to meet your class at the outdoor classroom to answer questions if he is available - just email him.  Also, below is another map with a key to where you can find some of the features I mentioned above.  I thought you might want the students to make their own, so I didn't include it above.  Also, I'll discuss the big boulder rocks in a later post.

Map of some of the fossils and rock features around our pond.

Japanese Quince

Every year about now I put on a few extra sweaters, check the weather forecast for snow, and go outside to look for.....flowers??!  Yes, that's right: flowers!

Japanese quince flower and flower buds.

It's time for Japanese quince shrubs to flower, and they are a welcome sight on these gray winter days.  Our outdoor classroom's Japanese quince shrubs are by the sidewalk near the entrance to the parking lot.  You can't miss them right now, as they are covered in blooms.

One of our two Japanese quince shrubs.

Japanese quince shrubs have an extremely unusual strategy for finding pollinators.  Their flowers are bee-pollinated, but there are absolutely no bees out today!  However, if you've lived in Middle Tennessee long enough, you've learned that we tend to have the odd warm day here and there throughout the winter.  When the weather warms up, beehives send out scouts to see if anything is blooming.  And for warm January days, Japanese quince have a monopoly on the blooming business, so any bees that are out will pollinate the Japanese quince.

Flower buds on a Japanese quince.

You may have already figured this out, but Japanese quinces are from Japan.  They were brought to the United States as an ornamental and edible plant centuries ago.  In the US, they are a slightly old-fashioned but well-loved garden plant.  You've already discovered their ability to brighten a dark winter day, but they also produce useful fruit, called a quince.  Quinces are relatives of apples and pears, and some types of quinces are well-loved in Asian and European cooking.  The quinces of our Japanese quince shrubs are small, hard and bitter, but they can be used to make excellent jams and jellies.  If these flowers are pollinated, we'll have some quince fruits later in the spring or early summer.  Watch out - Japanese quince shrubs have a few thorns to protect their quinces.

A sedum blooming in January.

There is another strange bloomer at the outdoor classroom right now.  It's called sedum, and it's growing right in the middle of the waterfall above the pond.  Sedums don't usually bloom until later in February or March, so I'm not sure what this little plant is up to.  But plants have variations just like people do.  Where people might have different hair colors, plants might have different blooming times.  If January turns out to be a good time for this sedum to bloom,  it will make lots of seeds and pass the early-blooming trait on to the next generation of sedums.  Next year there will be more early-bloomers.

Meet the Juniper (AKA Eastern Red Cedar)

Middle Tennessee is known for its cedar trees.  We even have a state park called Cedars of Lebanon.  The trouble is, the trees we call cedars are actually a type of tree called a juniper.  Our cedars have all the plant parts and structures of junipers, yet we call them Eastern Red Cedars.  Names are difficult to change once we get used to them, but I'm going to call our cedars junipers in this post.  The scientific name of our Middle Tennessee junipers is Juniperus virginiana, meaning juniper of the Virginia region.

Meet one of the junipers at our outdoor classroom.

Junipers have a million interesting characteristics.  My favorite thing about them is the difference in their immature and mature foliage (leaves).  Their mature leaves are smooth, rounded overlapping scales like you see in the picture below.  Junipers' immature foliage is sharp and spiky.  The easiest way to tell if foliage on a juniper is young or older is to close your eyes and feel the difference.  Fortunately, junipers are evergreen trees, so this is a great time of year to investigate their foliage.

Mature growth on a juniper.

Below is a juniper tree whole foliage is almost entirely immature.  It is about as big as the juniper in the picture above, so it must be about as old.  Spiky immature foliage protects young junipers from being eaten by deer or other animals.  I noticed the tree below was damaged and had its main stem cut.  Perhaps the tree is maintaining spiky, defensive foliage in response to what must have felt like a big bite to the tree (if trees could feel).

Spiky immature growth on a juniper.

On the branch below, you can see both mature foliage on older growth and immature foliage on new growth.  You can also see the cutest, tiniest cones you ever saw on an evergreen tree.  Juniper trees have two varieties: just like humans, they come in male and female forms.  Males trees produce cones like the ones you see below.  Female trees produce slightly larger purple cone-structures we call berries (because they look like berries).  Female trees must be larger before they can produce berries, so I didn't see any berries on our juniper trees, but we should have some in a few years.  We'll have to wait a few years to find out if any of our junipers are females.  Juniper berries are technically somewhat edible, but they have such a strong flavor that they are used mostly as a spice or flavoring.

Male cones, mature growth and immature growth on a juniper.

Below is the real prize.  I found one of these at the outdoor classroom, and I'm not telling where - you're going to have to find it!  No, it is not a piece of gum that someone stuck in the tree.  It is a fungus called cedar apple rust.  It grows on junipers (ok, cedars) for half its life, and it grows on apple trees for the other half of its life.  On junipers, it forms brown hard globs for most of the year.  After a warm spring rain, each of the dimples in the brown glob will sprout a bright orange spaghetti-shaped strand (I'm not making this up!).  The orange things produce spores that float away on the wind, land on a growing apple, and make the surface of the apple look splotchy.  The apple-stage of the fungus then makes spores that float and land on a juniper.  And you thought human life was complicated!

Juniper with cedar apple rust.