Page:Popular Science Monthly Volume 74.djvu/609

Rh Assuming the foregoing theories to be true, we can now trace the probable development of Okefinokee Swamp. When the ridge was thrown up across the shallow trough which had been Suwannee Strait it naturally created a basin behind it, which must have quickly filled with water, forming a large shallow lake. This lake then began to fill with vegetation, as many other shallow lakes and ponds in temperate regions are doing, and gradually took on the aspect it has to-day, which will be described more in detail below, under the head of vegetation. A glance at the map will show how the waters are dammed up by the ridge, the straight eastern border contrasting with the very irregular western border of the swamp.

The drainage of the region presents some peculiar features. Okefinokee Swamp is approximately on the watershed between the Atlantic Ocean and the Gulf of Mexico. In dry weather the Suwannee River seems to be its only outlet, but at other times some of the water may be discharged into the Atlantic through the St. Mary's. Being about on a watershed, the drainage area of the swamp is rather small, including only a few hundred square miles outside of the swamp itself. Its tributaries are practically confined to Ware County, on the northwest, and none of them exceed twenty miles in length. As the swamp is a few hundred feet vertically and a good many miles horizontally from any limestone, subterranean inlets and outlets are out of the question. The color of the water in the swamp and in all the streams in the vicinity shows it to be entirely free from lime as well as from mud.

The courses of the Satilla and St. Mary's Rivers in the neighborhood of the swamp are rather peculiar. Each after passing through the Okefinokee Ridge turns and flows parallel to the coast for about thirty miles, in the trough between the two low ridges mentioned, and then resumes its eastward course to the sea. The circuitous channels of these rivers must have been formed at the time of the Columbia submergence of the coastal plain if not before, for in such a flat sandy country there is practically no erosion going on at the present time, and such phenomena as stream-capture are unknown.

A pretty accurate estimate of the climate of the Okefinokee can be obtained by taking the averages of the figures for Waycross, Ga., and Macclenny, Fla., which lie on opposite sides of the swamp and at about the same distance from the Atlantic coast. Summed up by seasons, the average temperature and total rainfall are as follows: