128 Papers from the Marine Biological Laboratory at Tortugas. 



Darton was unable to determine definitely the age of the series overlying the 

 limestones, but the organic remains from 800 to 915 feet suggested Miocene age, 

 while foraminifera between 400 and 800 feet indicated that the beds whence they 

 came are also probably of Miocene age. 



This record shows that the top of the Vicksburg group (Lower Oligocene) 

 Hes between 915 and 1,000 feet below the surface at Palm Beach. The great thick- 

 ness of quartz sands is the most noteworthy feature of the record. 



Key Vaca. — Two wells were sunk at Marathon, Key Vaca, one reaching a 

 depth of 435 feet, the other 700 feet. The combined records of the two wells gives 

 the following section; 



Record of ivells of Florida East Coast Railway, Marathon. 



Description. Feet. 



Reef rock o to 105 



Hard to soft white limestone, with much white marl 105 148 



Soft white limestone with shell casts 1 148 150 



Medium hard white limestone, shell casts and shell fragments j 150 155 



Soft white limestone with quartz grains, proportion of quartz increasing with depth, 



shell fragments and casts 155 176 



Medium fine white quartz sand containing numerous irregular nodules, with yellow- 

 ish marly sand at 210 to 215 feet : 176 230 



Quartz sand in a varying proportion of limy mud, sand grains colorless, mud yellow- 

 ish to dark green; streaks and beds of friable sandstone containing shell casts; bed 



of oyster shells at 240 feet 230 300 



Quartz sands or beds of soft, friable sandstone containing shell casts; streaks of dark 

 green limy clay, 306 to 310 ft.; beds of shells, few determinable fossils, probably 



Miocene, 378 to 390 .' . 300 400 



Quartz sands as below 230 feet; beds of soft friable sandstone with shell casts; gravel 

 bed with much worn pebbles up to 40 mm. long; tough green limy clay, at 407 to 



4 1 o feet ] 400 43 s 



Quartz sands with little sandstone, tough dark clay in occasional strealra j 435 700 



While the many samples of drillings from this well show the lithology of the 

 formations penetrated, they give much less satisfactory evidence as to geologic 

 age. The sands below 176 feet yielded but a small variety of determinable fossils. 

 An occasional claw or carapace of a small crab or a few barnacle plates were the 

 only organic remains noted in going through many feet of sand. The friable sand- 

 stones contained many casts, internal and external, of pelecypod shells, the external 

 casts being of sandstone, the internal of more clayey material. These casts, while 

 numerous, were not sharp enough to be of diagnostic value. 



The shell beds yielded a small variety of species. T. Wayland Vaughan 

 identified five species, including pectens and an oyster, which were probably 

 Miocene, from collections between 375 and 420 feet. 



Thus the Key Vaca section, while it shows limestone. Pleistocene, and sands 

 probably Pliocene, gives no data for separating Pliocene from Miocene. The 

 coarseness of the sands, their barrenness and the character of the few detenninable 

 fossils between 176 and 400 feet indicate shoal water and strong currents. No break 

 in deposition is determinable. 



Fossils from Marathon Well, Key Vaca, were identified by T. W. 

 Vaughan, as follows: 



Depth 375 to 400 feet: Turritella variabilis Conrad; Ostrea, appar- 

 ently a new species; Pecten sp. fragment, probably P. madisonius Say; 

 Pecten sp. fragment, very near P. humphreysi Conrad; Pecten sp. young, 

 apparently P. eboreus Conrad. 



Geologic Horizon: Although the number of species is small, and 

 positive specific identification can be made in only one instance, the 

 fauna has a distinctly Miocene facies. The series of Pectens represented 

 by madisonius, humphreysi, and eboreus occur in association only in the 

 Miocene. 



