132 PROCEEDINGS OF WASHINGTON MEETING. 



Feet. 



1. Well-defined Lafayette sand, as seen on St. Augustine road and northward 



to Monticello ; water-bearing 40-60 



2. Solid, impervious sandy clays, very dark red ; seen in washes; pierced in 



deep well at Weelaunee; no fossils, no stratification lines, but traces of 

 both ; not water-bearing* 30-50 



0. Limestone, sometimes pure, sometimes very impure ; full of fossils, among 



them Orbitulites floridana, a Hemicardium very numerous (species un- 

 known), and many shells of Helix, Pupa, and other land snails ; burnt 

 for quicklime at Weelaunee; considered equivalent to Wakulla rock of 

 Tallahassee and Lloyds, and there approaches 100 feet ; here penetrated 

 in Weelaunee excavation (without getting through ) 50 



Between the locality of the above section and Tallahassee the St. Augustine road 

 crosses that part of the depresssed surface, south of Chaires station on the Florida 

 Central and Pensacola railway, known as the "natural bridge of St. Mark river." 

 All around the surface sounds cavernous to the tread, and there are numerous sinks 

 in the vicinity. 



From this part of the St. Mark country, at an ever-increasing distance from the 

 high hills of Lafayette sand, diverges a low terrace of Columbia sands overlying 

 silicious limestones and sandstones of no great thickness ; and this arenaceous rock 

 crosses all the small streams which empty into Apalachec hay. beginning at Aucilla, 

 by natural bridges; and this ancient beach line marks the boundary in that direc- 

 tion of the Chattahoochee embayment in its most extended definition. On Fen- 

 ahollowa river only the bridge has been washed away, hut enough remains to iden- 

 tify the old natural structure and its locality. 



A section at the natural bridge on Steinhatche.ee river (10 to 12 miles from its 



mouth), the easternmost of the series, will illustrate the system; and will at the 



same time well illustrate the relations of the older and the newer Tertiary rocks of 



Florida : 



Feet. 



1. Sands resembling the Columbia 6 



2. Impure silicious limestone, with a few fossils (as seen eastward at Howard's 



sink and the big slough one mile east of river) ; the dip is westerly, and its 



thickness increases from 2-4 feet to 8 



:!. A sandstone (no fossils), thin and broken at Howard's I5 miles eastward: 



getting thicker westward toward bridge ; probably 3 



4. Hard sandy marl, full of fossils; among them a Spatangus and two echinoids, 



at Howard's sinkf 2 



5. Not seen at the natural bridge but well seen at Howard's sink, Ik miles east, 



in the river, 1-2 miles north, and at 8-Mile creek, 4 miles northeast of bridge ; 

 a soft limestone easily eroded, filled with a Pecten (thought to be P. per- 

 planus) and innumerable reservoirs of Nummulites ( A", wttcoxi '.') 20 



* In genesis this is believed to >»■ a leached, oxidized ami altered marl, a kind of formation com- 

 mon in Florida, and proposed to be called amurcaceous, from amurco, the residuum of fruit or 

 olive press — that is, where the insoluble material of a 1 >• - « I retains the place of original deposit, but 

 is altered by meteoric waters. 



f These four members constitute the arch of the bridge. Tw iles north of the bridge the place 



of number l is tilled by an Ostrea l>e,l lying upon number '<, the shells resembling O. virginiana. 

 Paleontologists are m>i com inced that the fossils of numbers 2, 3 and I of this section are Miocene; 

 they may represeni an upper layer of the Eocene (Vicksburg) limestone, 



