Georgia Geology for Archaeological Purposes

 Archaeology is the study of human (pre)history through the materials and physical remains left behind. Personally, I study the prehistoric American Indians of the Southeast, specifically Georgia. The study of these cultural materials such as projectile points, ceramics, axes, celts, flakes, and other tools used by the native cultures. Each of these artifacts were constructed from local or regional resources around the state (although it was not a state thousands of years ago). This post will be to list and describe the many types of materials used to create cultural objects used by the Native Americans of the Southeast.

In these instances, archaeology gathers a lot of data from its sister-science of geology. Rocks, chert, and other material types are studied and placed in a local map. For example, one projectile point is a reddish-yellow hue and another is black and white. As archaeologists, not only can we look at the shape of the point to give an estimated time period it may have been made/used (should there still be a stem remaining), but by being aware of the material it was made from, archaeologists can also attempt to place the chert material to a specific region of Georgia or even different states or regions. (For instance, as I will show later, the reddish-yellow chert would come from the Piedmont region, or middle, of Georgia. The black and white would possibly have come from the Ridge and Valley region of Northwestern Georgia).

CHERT

The first types that I will discuss are chert types of Georgia’s physiographic provinces. Three regions have resources that are most commonly used as chert in Georgia: Ridge and Valley, Piedmont, and Coastal Plain. Each region has distinct variations and quality of chert. Other provinces include the Appalachian/Cumberland Plateau in the Northwestern corner of Georgia. This plateau features mostly sedimentary rocks such as shale, coal, sandstone, limestone. The last physiographic region is the Blue Ridge region that includes metamorphic and igneous rocks, most importantly soapstone (steatite), copper, lead, and marble. The next few sections will go into detail on the distinct versions of chert that are typically found in prehistoric contexts in Georgia.

map
Physiographic Provinces of Georgia. Those listed are discussed throughout this essay. Cumberland/Appalachian Plateau and Blue Ridge are not used. Source: http://narsal.uga.edu/gap/georgia

Ridge and Valley

This province in located in the Northwestern portion of Georgia, just below the Appalachian/Cumberland Plateau. Chert in this region is high in quality. Colors stay within the black to white spectrum, with some rare light browns. 

rv
Ridge and Valley Chert, varies from black to grey to white, high in quality.

Piedmont & Fall Line (includes heat treatment)

The Georgia Piedmont encompasses the entire central region of the state, from Columbus to Augusta. Located between it and the next physiographic province, the Coastal Plain, is the Fall Line, a geological border that is a mixture of the two. For archaeological purposes, this area is seen as the best of both worlds, including resources from both regions. The Piedmont province is fertile farm land with productive forests, rivers, streams, and shoals. The varied geology of the region produces diabase, amphibolite, rhyolite, metadacite, quartz, daltonite (which will all be touched on later), and fall line chert. Fall line chert is a very distinctive, yellowish colored that can sometimes be heat treated, causing the chert to turn red.

Coastal Plain (includes heat treatment)

Our last province, which reaches the southern half of Georgia is the Coastal Plain province. This chert type varies greatly in quality, some high and some quite terrible. The color changes from a white-ish hue to beige to brown. Coastal Plain is also found heat treated, which adds more color variations, usually red but also blue, purple, pink, and even sometimes a greenish tint.

GEOLOGY

Metadacite

A light stone, it is usually grey in color with sandy mottling. Examples can range from thin to medium in width. It degrades rather quickly, which leads to rounded edges. Usually found in the Piedmont region of Georgia.

meta
Metadacite examples

Amphibolite

Amphibolite, also known as Greenstone, is prominent in the Piedmont region. A rather dense, smooth rock, it was often used as atlatl weights, and also for ceremonial purposes (celts, etc.).

amph
Amphibolite/Greenstone example.

Diabase

Diabase is a heavy, grey stone with thin sandy mottling. These were often used for hammer stones, axes, and other tools. It also occurs in the Piedmont.

d
Diabase example

Soapstone

Soapstone is a popular rock even today. Because of its heat retention, it was often used as a heating rock in prehistoric time periods, and can even be seen today as bowls or countertops. It ranges in hardness but is usually quite durable and carvable. Soapstone is found in the Blue Ridge province of Georgia.

Rhyolite

Rhyolite comes from the Piedmont and is a grey to greenish grey rock, it often oxidizes to a lighter gray/white color. It is usually smooth to the touch, and often rather thin.

rhy

And that concludes my VERY general and brief overview of common types of Georgia material found in archaeological contexts. This is by no means an exhaustive and extensive review, there are many that I did not include. But I hope you enjoyed and also learned a few things! Below is a list of readings you may find useful about Georgia and archaeology. Until next time!

Georgia Encyclopedia features great articles by scholars in their fields on Georgia natural and cultural history. Here is a link for the Geography and Geology of Georgia, and here is a link for Georgia’s Historic and Prehistoric Past. This site offers a beginning and general overview for those that are interested in Georgia’s past.

Here is link for an intermediate read by the Georgia Department of Natural Resources on the Ecological Framework of Georgia.

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