6o4 



THE POPULAR SCIENCE MONTHLY 



The internal structure of the Okefinokee Eidge is not its least in- 

 teresting feature. In the big ditch at Camp Cornelia, as well as at the 

 crossings of four railroads (three of them shown on the map and one 

 a little farther north), there occurs beneath a few feet of white sand a 

 chocolate-colored or almost black material of unknown depth, known 

 locally as " hardpan." No analysis of the hardpan is availalile, but 

 when pulverized in the fingers it feels like nothing but sand. Its dark 

 color is doubtless due to vegetable matter, with a little cement of iron 

 oxide or bog ii'on ore, which makes it so hard in the mass that dynamite 



Jackson's Bay (outer edge). 



was used in removing it, it is said. ISTo recognizable organic remains 

 were noticed in it, but a faint horizontal stratification could be detected. 

 The aspect of the hardpan is so similar to that of the subsoil of existing 

 salt marshes that its origin is not hard to guess. 



Although this peculiar formation may not be confined to the Oke- 

 finokee Eidge, its extent is evidently limited ; for in railroad cuts 

 around Waycross and Folkston and in Camden County and elsewhere 

 the ordinary reddish Pliocene loam can be seen near the surface, with- 

 out any signs of the black hardpan. The hardpan was doubtless 

 formed in some preliistoric swamp or marsh occupying a somewhat 

 larger area than Okefinokee does now — perhaps the " Suwannee 

 Strait " of geologists,® which is supposed to have separated Florida from 

 the mainland in Miocene times. It seems to have no effect on the vege- 

 tation above it, which is Just like that of the ordinary flat pine-barrens 

 underlaid by the loam. 



°See Dall, Bull. U. S. Geol. Surv., 84: 111, 121-122, 126, 1892. 



