L. C. Johnson — Structure of Florida. 233 



Bridge " on Santafe River is an excellent example. In places 

 above the surface over which runs the public road, there are 

 old arches, once filled by the current of the river, before the 

 excavation of the lower tunnels now occupied by it. The 

 material of the present and of the old arches cannot be dis- 

 tinguished from softer varieties of the same formation in Ala- 

 bama and Mississippi, which is true also of the harder mate- 

 rial used as a building stone. 



, Some two miles south of the Natural Bridge and not far 

 from the Noonanville road, though at an elevation considera- 

 bly greater, in a quarry still used, is a stone exactly like that of 

 which chimneys are built in Conecuh and Covington Counties, 

 Alabama, and in Wayne and Jasper Counties, Mississippi. It 

 is the same stone also that is used for like purposes in Marietta, 

 Jackson County, Fla. 



Another fact worth noting of this quarry near the Santafe, 

 is that the N eocene formations to be mentioned farther on 

 seem to rest directly upon this building stone, without the 

 intervention of the Nummulitic limestone or of the usual 

 layer of silicified rocks, common farther south and west. 



Another locality like the rotten rocks of the Natural Bridge, 

 yielding millions of Orbitoides Mantelli and Peeten Poulsoni, 

 is the William's Sink near Noonanville. The " Big Sink " or 

 " Payne's Prairie " near Gainesville is another — which has 

 already been mentioned for the interesting fact of its silicifica- 

 tions. For miles to the south the low level country is covered 

 with loose rocks and bowlders of the silicified upper layer. 

 Particularly may this be seen at and around Aredondo, near 

 which also is the " Hogtown Sink " — showing a perfect repeti- 

 tion on a larger scale of the facts of the " William's Sink." 



Not to attempt to enumerate all the occurrences of such 

 exposures, it will be sufficient to say that the most southern 

 actually seen, are at Pemberton's, Pasco County, and on the 

 head waters of Hillsborough Piver in Polk County, Sec. 27 

 and 28, T. 26, P. 23 — which, till further advised, may be set 

 as the southern boundary of Eocene exposures. 



It might be objected that the " Gulf Hammock " region of 

 the west has sinks as well as this central region. True, and 

 there are also a few highlands and lakes at the west. But 

 neither exhibits a fair and general average of the Gulf region. 

 Instead of u Gulf Hammock" it might be called the "region 

 of springs." In the lowest portions of it (and it is generally low) 

 there are many of those great springs, which are the outlets of 

 the underground rivers. In the central region there are no 

 springs — no rivers. The Suwanee and the Santafe cut across 

 it, but do not rise in it. All the other streams rising in Neo- 

 cene sands are small and end in enormous cavities which swal- 



