28 
FLORIDA STATE GEOLOGICAL SURVEY. 
of the Florida Geological Survey during the past few years. 
The land pebble phosphates are found in southern Florida in 
Polk and Hillsboro Counties. This paper relates to the hard rock 
deposits only, the pebble deposits not being included in the dis¬ 
cussion, although their approximate location is indicated on the 
map. No attempt is made on this map to show the location of 
the low grade phosphates, which occur extensively in central Flor¬ 
ida. 
The matrix in which the hard rock phosphate is imbedded is 
extremely variable. The formation includes a mixture of 
materials from various sources and of the most diverse character, 
further complicated by pronounced chemical activity within the 
formation itself. The prevailing phase of the formation is feebly 
coherent, more or less phosphatic, light gray sands. Aside from 
these sands the principal materials of the formation are clays, 
phosphate rock, flint boulders, limestone inclusions, pebble 
conglomerate, erratic and occasional water-worn flint pebbles, 
vertebrate and invertebrate fossils, and occasional pieces of 
silicified tree trunks. 
Th$ gray sands may be observed in every pit that has been 
excavated in this section. Moreover, from drill and prospect 
holes it is known that these sands occur very 'generally over the 
intervening or barren area. The sands are of medium coarse 
texture, the grains being roughly angular. The amount of phos¬ 
phate associated with these sands is variable. Upon prolonged 
exposure, as seen in numerous abandoned pits, these sands oxidize 
at the surface, assuming a pink or purple color. When affected by 
slow decay and by water, carrying more or less iron in solution, 
thev become reddish or ochre yellow in color. Lithologically these 
sands resemble closely the gray phosphatic sands of the Alum 
Bluff formation as seen at the type locality at Alum Bluff, on the 
Apalachicola River. 
The clays in this formation occur locally as clay lenses im¬ 
bedded in the sand, or separating the sand from the phosphate 
rock, or overlying the phosphate rock. The clays are often of a 
light buff or blue color. When lying near the surface, however, 
they often oxidize to varying shades of red. The relative amount 
