Geology

Stone Mountain                  Example of mountain weathering

Mountain Geology:
Stone Mountain is one of the largest granite formations in the east. It exposes 7.5 billion cubic feet of rock. The nearby Mount Panola and Mount Arabia are similar to Stone Mountain though smaller. Stone Mountain formed 300 million years ago deep underground during the formation of the Appalachian mountains. The shifting of the earth’s crust beneath the continents created heat and friction which melted a large amount of rock below the surface. This magma (melted rock) slowly hardened into granite and remained hidden beneath the earth’s surface for millions of years. The granite was eventually exposed as the miles of land on top of the dome washed away with time and weathering.

Granite is an igneous rock because it was formed by crystallization of magma. The granite at Stone Mountain consists of quartz, mica and feldspar.

Granite Outcrop Ecology:
Unique plants can be found on Stone Mountain, plants which are rare across much of our state. Life on a granite outcrop can be very stressful because of exposure to the elements- rain, wind, sun, etc. Very few species can grow on the rock and there is a timely period of succession before a tree will ever take root on the granite. Succession describes the stages of plant growth, which occur before a mature plant community is established on the stone. The first organisms to grow on the rock are lichens. These are part fungi and part algae and live together by sharing their resources.

Crustose lichens on mountain surfaceThe lichens can wear away depressions in the rock allowing soil to gather and plants to grow. Mosses follow lichens in succession and as more soil gathers more plants and eventually trees will root in the shallow soil. Some of the trees which can be seen growing on the mountain include Loblolly Pine, Red Cedar, Georgia Oak and Black Cherry.


The depressions at the very top of Stone Mountain seasonally gather water and can than provide the necessities for life. There are a few endangered plants, which inhabit these pools as well as small shrimp. The shrimp leave tiny eggs behind in the soil when the pool dries up and their young are able to hatch and can be seen when the area receives adequate rains.

 

Solution pits formingSolution pits-small pools

Granite outcrop animals include many types of insects- look carefully for the granite grasshopper in the summer- the pattern on his body blends in with the lichens and the rock! There are also small mammals like mice and voles and numerous songbirds. From the top of Stone Mountain vultures (buzzards) and hawks can be seen soaring.





Learn more at the Confederate Hall Historical and Environmental Education Center's geology exhibit.