Rock City Educational Resource Guide

Geology

Rock City Resource Guide in PDF format

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Geology of Rock City

Underlined words defined in Geology Vocabulary

Lookout Mountain is a landform with amazing geological phenomena. The top of Lookout Mountain is where you will find Rock City Gardens. Rock City Gardens is an amazing journey through time. The massive rocks of the garden tell the story of Lookout Mountain that many people do not know.

About 300 million years ago the area that is now Lookout Mountain was a shallow sea. The skeletons of the small creatures that lived in the seabed accumulated on the bottom, along with pebbly sand and shale, and were compressed in layers to form limestone rock. Limestone rock is a type of sedimentary rock. Sedimentary rocks have layers called strata that are compressed to form a solid rock. The process that forms a limestone rock is called lithification. This limestone rock is still at the heart of Lookout Mountain. 

The beaches became something different. Ocean waves and currents deposited sand on the beaches. Over time the sand was compressed to form sandstone. Sandstone is a sedimentary rock that is made of tiny
grains of quartz.

The sandstone that was formed can be seen on top of Lookout Mountain at Rock City Gardens. In the Grand Corridor at Rock City you have a chance to examine the sediments that make up the sandstone rocks. The grains that make up the rocks are different sizes but some of them are easily seen. 

At the same time the sandstone of Rock City was forming, Lookout Mountain itself was being born. Tectonic movements of the earth’s plates caused a series of powerful earthquakes. The plates pushing against each other buckled, pushing rock upwards to form what is called a folded mountain. You know these folded mountains as the Appalachian Mountain chain. The limestone of the sea formed the heart of Lookout Mountain and the sandstone beaches are at the top.

The sandstone atop Lookout Mountain has undergone erosion. Erosion is the process through which rocks are broken down and carried away.  Water, wind, plants, or ice can do this. Water can break down a rock as it flows over it or as waves wash upon the rocks. As the water passes the rocks, it carries it away bit by bit. Wind erosion is more common in dry areas like deserts. Wind blows dust and sand at rocks and the abrasive actions sculpt the rocks into amazing shapes. Plants can erode rocks as their roots work their way down into the cracks of the rocks breaking them apart. Ice is a very powerful force of erosion. Glaciers gouge out valleys and can completely remove a hill as they travel through an area. Ice can form in saturated pore spaces and crack the rocks. The rocks at Rock City have most likely been eroded by water that was flowing through the area millions of years ago. Also the roots of the plants on the trail are contributing to this erosion. A great example of an eroded rock at Rock City is the Mushroom Rock. Looking at Mushroom Rock you can see the layers in the rock that characterizes it as a sedimentary rock made of
sandstone. This is an example of the strength of sandstone.

You can also examine igneous rock at Rock City. Igneous rocks are formed when molten magma from deep inside the earth moves up towards the cooler regions. The magma cools and crystallizes to form the igneous rock.  Sometimes the magma is erupted from a volcano as lava and cools on the earth’s surface to form extrusive rock. The rock could also cool inside the earth to form intrusive rock. There are no volcanoes on Lookout Mountain.  The igneous rocks are seen at the Seven States Flag Court. The pedestals for the flagpoles are made of an igneous rock called granite.

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Crystals and Coral at Rock City Gardens
Underlined words defined in Geology Vocabulary

Walking through Fairyland Caverns you will see crystals across the ceiling.  The crystals you will see are not natural to the area but were brought in.  Crystals are solids that form in a regular repeated pattern and have the same arrangement of particles over and over throughout the entire structure.

Only if a mineral is allowed to grow without interference from other minerals will it form crystals. Minerals “grow,” or crystallize, from many types of solutions. Crystals may be formed from evaporating seawater, or from magma when lava cools. While growing, minerals may develop a distinct shape. You can examine the crystals in the Fairyland Caverns ceiling and count the faces of the crystals that are primarily either quartz or fluorite.

Crystals have:
1. An orderly and symmetrical atomic structure (repeated pattern of particles)
2. A definite chemical composition (growing without interference)
3. A definite shape with faces (flat sides)

As you are walking through Fairyland Caverns looking at the ceiling you will also find coral. This coral was brought to Rock City Gardens. Any coral that originally occurred at Rock City was broken up into bits millions of years ago to make the sandstone rocks that surround you. Coral looks like rock but it is actually a living animal. The coral you are looking at on the ceiling is actually the hard skeleton of what was once a living coral polyp. The coral grows over thousands of years as the hard skeletons build up. The skeletons are actually made of limestone – the same type of rock you will find at the heart of Lookout Mountain.

You will also see rocks that seem to glitter. These silvery rocks are made up
of thin sheets of material called mica. Aren’t they pretty?

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Environmental Education: Soil Erosion
Underlined words defined in Geology Vocabulary

At Rock City Gardens you have a wonderful chance to examine the effects of erosion on the sandstone boulders that are around you. The erosion that carved out the rocks is a natural process that has occurred since the earth’s beginning. At Rock City Gardens you can stand on Lover’s Leap and see ridges that have been carved into the side of the mountain by erosion. 

Not all erosion happens the way it should. Soil erosion is a natural process where soil is moved by wind or water. In recent years, accelerated soil erosion has become a problem. Deforestation is a major cause of soil erosion.  Trees have deep roots that hold the soil in place. When the trees are removed, the soil is loosened and can easily be washed away. Extensive farming also causes soil erosion. Land that has been farmed too much is easily eroded away and loses nutrients. After land has been farmed too much, even if it is not eroded away, it is no longer able to sustain plant life. Building homes and roads also damages soil. During construction the land is left bare to rain and wind, making it easier to become eroded.

Soil erosion (and degradation) can leave devastating effects. Excessive rain in areas that have been eroded can result in landslides or mudslides.  Farmers lose land that is used for producing food. Silt and mud can be washed down streams and build up downstream causing problems for people in that area. Silt and mud can be washed into the ocean where it settles on the bottom. Organisms that live in the ocean are killed by the change in their
environment.

Farmers can help to prevent soil erosion by not over-using or over-grazing land. They can also use crop rotation, allowing plants to decay in soil as a natural fertilizer. Plants play a very important part in the prevention of soil
erosion. Keeping natural plants in their area and allowing trees to remain is a good way to prevent soil erosion. Plant roots hold the soil in place but they also add their organic material to the soil, which helps to keep it healthy
and productive.  Even in your hometown there are probably places that have experienced soil erosion. You can help prevent it at your home by planting plants in barren areas. You can help prevent it by not allowing barren spots with no grass.  You can also help by making sure that during a rain shower any areas of exposed soil are protected and not washed away.

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Rock City Geology Vocabulary

Coral A polyp found in the ocean. Coral creates hard skeletons that over years build up to make a coral reef.

Crystals A solid substance with a regular pattern and symmetrical faces (or sides.)

Erosion The process by which weathered materials are carried away by wind, water, or glaciers.

Igneous Rock Rock formed by the solidification of molten magna.

Landform A feature on the earth’s crust. Examples of landforms aremountains, valleys, plains, and plateaus.

Lithification The process of pressing layers of sediment until they becomesolid rock.

Metamorphic Rock Rock formed when other types of rock (sedimentary and igneous) are exposed to heat and pressure.

Quartz A crystal that is not easy to break down. It is made of oxygen and silica. Sand is very small pieces of eroded quartz.

Rock Cycle A continuous process that changes old rocks into new.

Sandstone A type of sedimentary rock made mostly of quartz.

Sedimentary Rock Rock formed from sediments that have been pressed together over time to make solid rock.

Strata Layers of sediment that are pressed together to make sedimentary rock.

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