8 E. H. SELLARDS 



To what extent the three divisions of this section represent dis- 

 tinct time intervals, and, on the other hand, to what extent they 

 may intergrade and thus express continuity of time, is discussed 

 subsequently. These divisions are sufficiently well marked to be 

 recognized throughout the greater part or all of the section, and 

 serve as convenient markers in the exact placing of fossils. 



The marine deposit, No. i of the section, is common to this 

 part of the Atlantic Coast of Florida, and is known to extend both 

 to the north and to the south, being a part of an extensive shallow- 

 water marine formation which borders the Atlantic Coast in 

 Florida for a distance of 200 or 300 miles. This stratum is pre- 

 vailingly a shell marl, although it contains considerable sand, and 

 in places may consist wholly of sand of medium fine texture. A 

 large exposure, however, will scarcely fail to reveal the presence 

 of the marine shells. 



Stratum No. 2, on the other hand, is probably local, represent- 

 ing fill in the stream valley, although its time equivalent, as indi- 

 cated by the fauna, is found at many localities throughout the 

 state. This deposit in the stream valley averages 3 or 4 feet in 

 thickness, and consists chiefly of rather coarse sand, which at the 

 top as a rule grades into fresh-water marl. Within the stratum, 

 filling holes or channels in the underlying deposit, are found local 

 accumulations of muck, including often wood, sticks, acorns, 

 snail shells, and vertebrate fossils. As a rule the sand near the 

 base of this stratum is light-colored and distinctly cross-bedded, 

 the heavy minerals, including staurolite, ilmenite, and quartz, 

 being deposited in bands and in pockets according to the size of the 

 grain and the specific gravity of the minerals. From 2 to 3 feet 

 above the base of the stratum the sand loses its cross-bedding and 

 becomes dark in color, owing to the inclusion of organic matter. 

 At the top, as has been stated, the sand passes into marl, contain- 

 ing an abundance of land and fresh-water invertebrates. 



Stratum No. 3 consists chiefly of layers of muck and vegetable 

 material, alternating with layers of loose, nearly pure, light-colored 

 sand. This alternation of sand and muck is both abrupt and 

 frequent, the layers in places having only a thickness of from one- 

 half to 2 or 3 inches. At the top this stratum grades into a fresh- 



