Logo Mississippi State Geological Survey Bulletin 28
The Geologic History of the Vicksburg National Military Park Area




Notwithstanding the minor distribution of the Confederate and Federal armies at Vicksburg by Pemberton and Grant during the siege of the City from May 18 to July 4, 1863, the fact, nevertheless, remains that the major disposition of the forces was determined untold ages before by the Creator working through the agency of one of the Continental Glaciers in Canada and northern United States. This particular glacier, in passing over the bedrock of the region, ground some of it, as well as some of the rock material the ice was transporting, into a fine rock flour, which the flood waters from the melting glacier carried down the Mississippi and deposited as flood plain material. The westerly winds picked up this rock flour, after it had dried, carried it on to the east bluffs and uplands, and deposited it as a mantle rock that forms steep-sided valleys where streams cut into it. These valleys were the controlling factors in the distribution of the armies.

But this is beginning far along in the geologic history of the Vicksburg National Military Park region; in fact, near the closing stages of its history. Although this geologic history of the area does not stretch back to the most ancient eras of geologic time, it does reach millions of years into the past.

Perhaps this can best be demonstrated by giving all the major divisions of the geologic time scale:

Geologic time scale

   Cenozoic era
      Recent period
      Pleistocene period
      Pliocene period
      Miocene period
      Oligocene period
      Eocene period
   Mesozoic era
      Cretaceous period
      Comanchean period
      Jurassic period
      Triassic period
   Paleozoic era
      Permian period
      Pennsylvanian period
      Mississippian period
      Devonian period
      Silurian period
      Ordovician period
      Cambrian period
   Proterozoic era
      Keweenawan period
      Late Huronian period
      Middle Huronian period
      Early Huronian period
   Archeozoic era
      Archean period

Beginning with the Comanchean in late-Mesozoic, much of the subsequent material was laid down along the Atlantic and Gulf coastal plains, and is, for that reason, known as the Coastal Plains deposits. Save for some Paleozoic rocks along the stream courses in Tishomingo County, in the northeastern corner of the state, the geologic history of the beds at the surface begins in late Mesozoic time with the Cretaceous.

This was the time of the so-called Mississippi embayment, when an arm of the Gulf spread broadly over the southern part of the United States and reached as far north as the mouth of the Ohio River at Cairo, Illinois, or even slightly farther north. In this sea the thicker sediments were laid down along the old shore line which at the beginning extended almost north and south across the northeast corner of the state. As time elapsed and as the embayment became more and more filled with sediment the old shore line shifted farther toward the south and to a more nearly east and west position in the vicinity of Vicksburg. Here begins the detailed history of the Vicksburg area, but it calls for a more detailed time scale of later geologic time.

Later geologic time scale

Cenozoic era
   Recent period
   Pleistocene period
         Loess age
         Terrace age
   Pliocene period
         Citronelle age
   Miocene period
         Pascagoula age
         Hattiesburg age
         Catahoula age
   Oligocene period
      Vicksburg epoch1
         Byram age
         Glendon age
         Mint Spring age
         Forest Hill age
   Eocene period
         Jackson age
      Claiborne epoch
         Yegua age
         Lisbon age
         Tallahatta age
      Wilcox epoch
         Grenada age
         Holly Springs age
         Ackerman age
      Midway epoch
         Porters Creek age
         Clayton age

1The term Vicksburg was first applied to the rocks of this region by T. A. Conrad, Acad. Nat. Sci. Phila., Proc. 3, pp. 280-299, 1847.

Figure 1.—Falls in Mint Spring Bayou at the National Cemetery, Vicksburg. The rocks are correlated on the left and described on the right.&$151;Photographed January 9, 1935.

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Last Updated: 18-Jan-2007