SECOND ANNUAL REPORT—STRATIGRAPHIC GEOLOGY. 153 
or below sea level where they merge with the fossiliferous marls 
previously described. 
The gray sands are usually uncemented but locally the presence of 
iron oxide has transformed them to a dense concretionary sandstone 
which is almost as resistant as quartzite. Examples of rock of this 
kind are to be seen at several localities along the Louisville and Nash¬ 
ville Railroad north of Pensacola, and at various other places in the 
State. 
While sinking a well at Apalachicola the driller reported a pine log 
at a depth of 60 feet imbedded in incoherent sands which are prob¬ 
ably of Pleistocene age. Other examples of vegetable matter as well 
as logs have been noted at various localities in Florida. This suggests 
that swamps may have existed during the deposition of the sands, 
but the absence of any considerable bodies of peat imbedded in the 
deposits shows that the marsh conditions were of short duration; or, 
that the supply of sediment was sufficient to prevent the accumulation 
of thick layers of pure organic matter. Except near the coast, the 
thickness of the sands is seldom sufficiently great to mask the topog¬ 
raphy of the underlying formations and they rarely form any con¬ 
spicuous topographic features aside from the terraces and a few dunes 
and low ridges. 
Planorbis Rock:—Following the deposition of the main body of 
the gray sands, there appears to have been a number of shallow bodies 
of fresh water occupying the depressions in the surface of the newly- 
emerged sands. In these bodies of fresh water, there accumulated 
thin deposits of marl which differ from the earlier marls of this period 
in being composed of calcareous matter nearly free from sand. 
In this marl, the most conspicuous fossils are gastropods, especially 
those belonging to the genus Planorbis. While this rock may be in 
part post-Pleistocene, satisfactory subdivisions can not be established 
at the present time. This rock should not be confounded with the 
“Planorbis rock” of the Caloosahatchee River, which has been re¬ 
garded as Pliocene. The u Planorbis marls” of Quaternary age have 
been observed at Daytona, Sanford, and on the Santa Fe River, south¬ 
west of Fort White; and, according to Eldridge, 1 they occur in most 
of the “hammocks” between Kissimmee and Lake Okeechobee. 
The Quaternary deposits of the southern end of the peninsula and 
the keys will be discussed in a subsequent chapter by Mr. Samuel 
Sanford; and, hence, they will be omitted from the general discus¬ 
sions of the Pleistocene and Recent beds. 
Coquina:—One of the most common of the marine Quaternary 
deposits is the coquina which occurs at various points along the coast. 
1 Eldridge, Geo. H. Unpublished notes. 
