L. 0. Johnson — Structure of Florida. 235 



streams, and excavations from Georgia, as far south at least as 

 Okala and Levyville. It yields many springs. Among these 

 may be mentioned the "Magnesian Springs" of Simmons and 

 Brown near Hawthorne. The current here often brings out 

 fragments of shells and ferruginous particles. A great bed of 

 these shells with limonite may be seen exposed in the run of 

 Lochloosa Creek near the springs. 



Layer No. 4 — the buff and greenish clays — could seldom be 

 seen. A similar clay, but possibly a reworked later deposit 

 contains the great bone bed at Mixon's near Archer. These 

 fossils are all vertebrate and all silicified. Similar deposits are 

 found in many other places, and often as islands left by ero- 

 sion, and always resting upon Eocene rocks. Similar fossils 

 are found scattered (as already said) throughout layer No. 2, 

 and possibly may be found in still newer formations farther 

 south and east. 



This about concludes the matter. The Waldo formation 

 once understood, the stratigraphy of east and south Florida 

 may he understood. This formation is the basis of the " high- 

 pine" and "high-hammock" soils, and is one of the factors in" 

 the genesis of the lakes. The other factor is, of course, the 

 underlying rotten limestone, of Eocene age, with its sub- 

 terranean tunnels and rivers. To the last are due the sinks. 

 Wherever there is a sufficient thickness of the overlying Mio- 

 cene rocks and clays to choke up the sink, and arrest the draw- 

 ing of the superficial layers into the great hopper-shaped cen- 

 ters of erosion, a lake is formed. 



In the Central Lake Eegion, these bodies of water all 

 approximate a funnel-form in depth and outline. Many of 

 them have no superficial outlet. 



To the extreme south and southwest, Florida has many 

 other lakes not of this class and history : lakes which are all 

 connected with the streams and rivers, and are but remnants of 

 ancient lagoons and inlets of the sea of latest Tertiary and 

 Quaternary times. These are all comparatively low lying, 

 have firm bottoms of inconsiderable depth, and are not at all 

 connected with the underground drainage of the Yicksburg 

 rocks. 



For this reason the high lake region is a good mark of 

 Eocene limestone lying within about 100 feet of the surface ; 

 and the formation may be as safely located thereby as if there 

 were manifest outcrops. 



The southern lakes, like Thonotosassa, and Tohoptaliga, 

 have for their bed another phase or stage of the Miocene, 

 which for convenience may be called the Tampa formation, 

 constituting so thick a layer that the influence of the underly- 

 ing Eocene is not felt. The same is true of Tampa and Hilis- 



