A Few Notes

These images are scanned from the Geologic Map of Georgia (1:500,000) published in 1976 and re-printed in 1997 by the Georgia Geologic Survey. You may purchase this map -- and many other publications -- from the Geologic Survey Map Room in the Department of Agriculture building in downtown Atlanta, about one block southwest of the MARTA rail station at Georgia State University. At this writing (October, 1999) you may contact the Map Room at (404) 657-6127.

Map sheets are designated with North and East offsets from the lower left corner:

To produce images for these map pages, I:

• Cut the 1:500,000 Geologic Map of Georgia into rectangles approximately one degree on a side, adjusting the width of some eastern panels to avoid images with a small triangle of information in only one corner.
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• Scanned the resulting sheets at 300 dpi on a letter-size flatbed scanner, producing JPEG images which in some cases approached 3 Mb in size.
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• Cropped and resized the scanned images to fit a 640-pixel display width; sharpened, balanced, and compressed images to produce final image files smaller than 200 kb.

If you are loading these pages through a dial-up connection, please accept my apologies for the large size of some graphic files. I have tried to balance legible detail against file size; I think these images represent a decent compromise.

In geologic time, 1976 is not long past. In human time, we have greatly advanced our knowledge of Georgia's geology -- and processes that produced it -- in the quarter-century since this map was compiled. We now perceive the Piedmont's metamorphic provinces as a complex of thrust sheets, tectonic melanges, and scraps of crust and mantle from the vanished floor of an ocean we call Iapetus, ancestor of the Atlantic Ocean. We now see Georgia's granites mostly not as classic intrusive plutons but as shallow-rooted bodies, friction-melted from their surrounding rock as the Iapetus basin closed. We think that Georgia's southeast Piedmont -- and rock beneath the Coastal Plain -- is a fragment more closely related to Africa's ancestor continent than to North America. We now see long-term geologic changes as effects not of a vaguely-defined geosynclinal cycle taking place on the margins of stationary contintents, but of global movement of crustal plates, opening and closing ocean basins, and continents shifting in a massive centimegennial dance.

Amid such change, it's a marvel that a 1976 geologic map remains useful as well as a thing of cartographic beauty. Enjoy this one, and look forward to the next.

OK, maybe I'm laying it on a bit thick when I call this map "a thing of cartographic beauty." The Georgia Geologic Map was the first geologic map I ever saw, and it knocked my socks off. I still think it's pretty cool, despite its deficiencies.