Professor Earle Sloan, in his “Mineral Localities of South Carolina” (Bull. No. 2, ser. IV., South Carolina Geol. Surv.), has recognized the following divisions in the marine Pleistocene of the State:
6. Sea Island loams. 5. Wando clays and sands. 4. Accabee gravels. 3. Bohicket marl-sands. 2. Wadmalaw marl. 1. Ten-Mile sands.
Of these, the fossiliferous deposits referred to above appear to belong to the Wadmalaw marl. It may be confidently expected that somewhere along the South Carolina coast, beneath the beds bearing the vertebrate fossils, there will yet be discovered other Pleistocene deposits, probably shell marls, which belong to the Nebraska stage.
GEORGIA.
The only part of Georgia at present of interest to the student of vertebrate palæontology is that which lies immediately along the Atlantic coast and along a few of the larger rivers. The northwestern corner of the State is mountainous and probably contains little or no Pleistocene. The Coastal Plain extends landward to a line which starts at Augusta, on Savannah River, passes through Milledgeville and Macon, and ends at Columbus, on the Chattahoochee. A large part of this region is mantled by a deposit resulting from the decay of the underlying rocks. These deposits are of uncertain age, a part belonging probably to the Pleistocene, but the large part to the Pliocene or to still older Tertiary. The Pleistocene has not yet been differentiated from the remainder, and, in any case, has furnished no vertebrate fossils. For information on the subject the reader may consult McGee (12th Ann. Rep. U. S. Geol., Surv., pt. I, pp. 478–484), Spencer (Geol. Surv. Georgia, 1890–91, pp. 61–81), and Veatch and Stephenson (Bull. 26, Geol. Surv., Georgia, pp. 400–456).
The deposits in Georgia which can with certainty be referred to the Pleistocene form a broad belt lying along the coast and extending landward a distance of about 30 miles along Savannah River and about 60 miles at the Florida boundary line. For a description of these deposits the reader is referred to Veatch and Stephenson’s article in Bulletin 26 just mentioned, pages 424–456. These deposits are disposed in two terraces, a higher and older and a lower and younger. The older is named the Okefenokee formation, the younger the Satilla formation. The positions of these may be observed in the figure here presented, taken from Bulletin 26 above referred to (fig. 20).
The Okefenokee terrace has a breadth of 20 to 40 miles and an elevation of 60 to about 125 feet above sea-level. It forms a plain which Veatch and Stephenson describe as in general flat and almost featureless. It is dotted with cypress ponds and swamps, with here and there low ridges and hills of sand. Along the larger streams which cross the plain are found terraces supposed to have been laid down while the Okefenokee terrace was forming; they extend far back into the State. In neither the main terrace nor the fluviatile terraces have any fossils been found, except a little silicified wood.
Fig. 20.—The Coastal Plain of Georgia. Adapted from Veatch.
The Satilla Plain extends backward from the coast 20 to 30 miles and varies in elevation from 15 to 40 feet. On the landward side it ends in an escarpment which is taken, by the authors quoted, to be an old sea-beach. Along the large rivers it is continued as a series of terraces occupying a lower position than those of Okefenokee time. According to Veatch and Stephenson, this formation consists of unconsolidated clays, sands, and thin layers of gravel. The thickness averages about 15 feet, but may become as much as 45 or 50 feet.