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.

The Satilla deposits are fossiliferous. At various places, at some distance from the coast, sea-shells occur, especially shells of oysters. This shows that at times the plain, or at least some parts of it, has been under sea-water. Bones and teeth of vertebrate animals have been discovered at several localities, but at only two places have identifiable materials been secured. The region about Brunswick and that just south of Savannah have furnished important collections of vertebrate animals.

During the years 1838 and 1839 an attempt was made to construct a canal to connect Altamaha River with Turtle River at Brunswick. Some bones of large mammals were met with and came to the notice of Hamilton Couper, and through him became known to the scientific world. The most striking was the great ground-sloth, of the genus Megatherium, and which Leidy afterwards called Megatherium mirabile. At a more recent time, during dredging operations, probably in the harbor, other remains were found and turned over to the Geological Survey of Georgia. The fragmentary bones and teeth were identified by Mr. J. W. Gidley (Bull. No. 26, Geol. Surv. Georgia, p. 436).

The fragments of teeth regarded by Gidley as belonging to Mammut floridanum appear to the writer to represent Gomphotherium rugosidens, a species rather common in that region and belonging to the upper Miocene or Lower Pliocene. Four teeth identified as those of Physeter vetus or Physeterula neolassicus appear to be identical with Leidy’s Orycterocetus quadratidens; but this may be possibly the same as Physeterula neolassicus (=P. dubusi). It, too, is older than the Pleistocene. From the two collections have been determined the following list:

With the bones found in the canal was a femur 13 inches long, which Harlan described as Chelonia couperi, but which resembles more closely that of some edentate mammal. Gidley stated that the shark-teeth probably represent Eocene and Miocene species. This may be true, but the supposition is not necessary, inasmuch as species of all three genera are yet living on our Atlantic coast.

J. Hamilton Couper (Hodgson’s Memoir, pp. 37–40) has given an account of the topography and geology of the region through which the Brunswick Canal was being constructed (map [40]). On one of the plates of the work is a section from the ocean westward 21 miles. About 10 miles west of St. Simon’s Island the canal passed through Six-mile Swamp. This is connected at its northern end with Altamaha River, at the southern with Turtle River. The swamp has thus the appearance of a lake which has become filled with alluvial deposits. These consist of a compact clay, usually yellow and impregnated with iron. There are thin strata of soft, chalky marl and many fragments of petrified wood. At the bottom of this deposit were found the bones of Megatherium, Elephas, Mammut, Equus, and Bison. Beneath the clay stratum was sand with marine shells. Overlying the clay was a thin stratum of vegetable and sandy loam. The bones occurred at a depth of from 4 to 6 feet. In no instance, except when they had been washed out into the salt-water creek, was there any abrasion of the surface or incrustation of marine shells.

The geologist Charles Lyell (Second Visit, etc., vol. I, p. 347) stated that part of a skeleton of a megatherium, dug out in cutting the canal, was so near the surface that it was penetrated by the roots of a pine tree. As a considerable number of the bones of one skeleton were found together, Lyell supposed that a whole carcass had been floated down the river to the spot.

Even before remains of fossil vertebrates had been found at Brunswick, bones had been discovered at Skidaway Island, near Savannah. As early as 1823, S. L. Mitchill (Ann. N. Y. Lyc. Nat. Hist., vol. I, p. 58) announced the finding of teeth of Megatherium at this place. More than 20 bones of the same animal were reported from the same locality in 1824 by William Couper. In 1846 (Hodgson’s “Memoir on Megatherium,” pp. 25–30), Dr. Joseph Habersham published a list of the species discovered up to that time. Lyell (Second Visit, etc., vol. I, p. 313) gave an account of his visit to the locality and noted the species obtained. The following list appears to contain all found there:

The box-tortoise Terrapene canaliculata was described by the writer in 1907 (Bull. Amer. Mus. Nat. Hist., vol. XXIII, p. 850, figs. 5–7) on fragmentary materials found in the U. S. National Museum. These had been sent there by Dr. J. P. Scriven, who had been active in collecting the fossil vertebrates about Savannah. Whether the remains of this box-tortoise were found on Skidaway Island or in Whitemarsh Island is uncertain.

Besides these species, found on Skidaway island, two species, Mammut americanum and Mylodon harlani, have been found at Heyner’s (or Hainer’s) Bridge. This is about 7 miles south of Savannah, where the road crosses Vernon Creek (Lyell, “Travels in North America,” vol I, pp. 163–164). Here the stream is called White Bluff Creek. In order that the reader may get a clear understanding of the conditions at this important locality, a map found in Hodgson’s Memoir is reproduced (map [40]).

The whole region south of Savannah, between the mouths of Savannah and Ogeechee Rivers, is low and much divided into islands by streams connected with the rivers mentioned. A considerable part of these islands consists of marshes, which are usually overflowed by the tides. Most of the fossil bones were found along the southern bank of Skidaway River, in two places, apparently about 0.5 mile apart and near the western end of the island. On the map Hodgson has named the locality Fossilossa. Here Skidaway River made a bend which caused the bank to be eroded away, thus exposing the bones. According to Couper (Hodgson’s Memoir, p. 40), the bones were embedded in the marsh formation at about the level of very low-water. Lyell (Second Visit, etc., vol. I, p. 314) stated that the bones occurred in a dark peaty soil, or marsh mud, above which was a stratum of sand 3 or 4 feet thick; while below the peaty soil and below sea-level was sand containing many marine fossil shells, all belonging to species yet living on the neighboring coast.

The authors quoted state that at various places along the Georgia coast are found stumps of trees, cypress, cedar, and pine, in the deposits of the salt marshes and at a depth of from 2 to 4 feet below high-water. This is taken as evidence of subsidence in that region.

It is a matter of importance to know how those animal remains reached their place of burial. It has been suggested that whole carcasses had been floated down the streams and sunken where the bones are found. This is possible, but not probable. The peaty nature of the deposit inclosing the bones appears to be opposed to this view; nor could disarticulated bones have been washed down far from above, for they show no signs of attrition. The most probable explanation is that these animals lived and died about where their bones were discovered. At some past time the surface stood at a higher level than at present, although low enough to be more or less marshy. It probably supported a dense forest growth, and hither the species listed above resorted, with many others not yet discovered.

The animals inhabiting the region represent the same fauna found at so many places in Florida and Texas. The writer believes that they existed during the early part of the Pleistocene, approximately during the Aftonian interglacial; and that some of the species, as Megatherium, Mylodon, Equus, and Tapirus haysii became extinct before the advent of the Wisconsin glacial stage, probably a long time before this.