234 Z. C. Johnson — Structure of Florida. 



low them up, to be seen no more, till they rise again in the 

 Ocean, or by such outlets as Silver Springs to the east, and 

 Tarpon and other great springs to the west. 



The Neocene terranes of Florida begin somewhat farther 

 west than the line, assigned them on our latest geological maps. 

 Instead of Trail-Ridge, they can claim the Weldon and Gaines- 

 ville highlands for their western boundary. 



A fair section, verified from several partial exposures, and 

 many excavations and borings, gives us for the Gainesville 

 highlands : 



1. Unimportant and variable layer of detrital 



accumulations and soil 1 to 10 feet. 



2. The "Chimney rock," or Waldo formation 



having Miocene fossils, and generally 

 phosphatic, not less than 10 feet, and pos- 

 sibly 50, average ... 30 feet. 



3. Ferruginous sands, with chalcedonized shells 



of Ostrea and others, and in places limo 



nite 10 feci. 



4. Greenish and buff clays — sometimes indu- 



rated, and sometimes with fossils 1 to 50 feet. 



Total 100 feet. 



Layer No. 1 requires no specific description. Where the 

 sand is very deep the soil is usually thin. Where sufficiently 

 thinned off to permit the influence of the underlying forma- 

 tion, the fine " high-hammock " lands are found. 



Layer No. 2 in places called the " chimney-rock " from a 

 popular use of one of its constituents — is the site and source 

 of the phosphatic rocks of this part of Florida. In places it 

 has suffered much erosion, and the reworked material has often 

 been redeposited in beds of uncertain age, making a conglom- 

 erate with clay, bones, and nodules of the rock. Simmons's 

 phosphate bed near Hawthorne is a good instance, and the 

 " Devil's Mill-hopper " west of Gainesville is another. Undis- 

 turbed and in situ, among other places, it may be seen near 

 Waldo, at old Fort Harlee in Preston's marl bed. 



The fossils of this locality are innumerable, but mostly as 

 casts of the interior of shells or moulds of the outer surface. 

 Vertebrate remains are unchanged or only silicified, and so also 

 are Ostrea and Pecten among invertebrates. Of the latter, 

 easily recognized, are Pecten Madisonius and another large 

 one ; casts of at least two large Carditas ; a large Venus very 

 much resembling V. mercenama but of coarser outlines ; a very 

 large Balanus, and many casts of gasteropods. 



Layer No. 3, as said elsewhere, is the source of the limonite, 

 and of the peculiar ostrea-chalcedonized — found in many 



