286 FLORIDA GEOLOGICAL SURVEY-SEVENTH ANNUAL REPORT. 
dated as to' necessitate mapping according to the predominating 
type. In places the Johnston fine sand grades into' the uplands so 
imperceptibly that it is difficult to determine the exact boundaries 
between the overflowed land and the upland, there being a close 
resemblance between this type and the higher lying Portsmouth fine 
sand. Where the Johnston fine sand grades into the Portsmouth 
fine sand, the typical Portsmouth hardpan is frequently present, even 
though the area is regularly overflowed. On the lower areas, near 
the stream banks, the black surface layer is sometimes only '2 to 4 
inches deep and the soil often has a decidedly loamy feel on account 
of the greater silt content. These silty areas, however, are too small 
to be separated on the map from the typical. 
This soil occupies the flood plains of the smaller streams of the 
county. Most of the type is elevated only a foot or two above the 
general level of the streams, and during seasons of heavy rainfall it 
is entirely inundated. The material consists of alluvial deposits de¬ 
rived from the upland soils of the drainage basins of the streams 
along which the type occurs. The topography is level, with only an 
imperceptible slope toward the stream channels. There are a few 
very slight. ridges and swales. In the southwestern part of the 
county there are two narrow strips of soil similar to this type, which, 
although apparently of alluvial origin, stand above overflow some¬ 
what like second-bottom soils. The relatively high position occu¬ 
pied by these areas has resulted from, the formation of limestone 
sinks nearer the stream. 
The Johnston fine sand supports a characteristic natural growth 
of shortleaf and longleaf pine, slash pine, magnolia pine, palmetto, 
scrub varieties of holly and oak, titi, gallberry, bay, iron wood, haw, 
water or turkey oak, sweet gum, ash, magnolia, hickory, myrtle, and 
pecan. 
Practically none of the type is cleared for agricultural use. The 
merchantable timber has in most cases been removed, and the re¬ 
maining longleaf pine is “boxed” for turpentine. The type is used 
largely for pasture. Water stands over much of this soil during a 
large part of the year, and artificial drainage is necessary before it 
can be utilized for farming. 
The following table gives the results of mechanical analyses of 
samples of the soil and subsoil of this type: 
