THfi FLORIDA PHOSPHATE DEPOSITS. 33 
THE LAND PEBBLE PHOSPHATE—BONE VALLEY 
FORMATION. 
LITHOLOGIC DESCRIPTION. 
The land pebble formation to which Matson and Clapp applied 
the term “Bone Valley Beds” was briefly described in the Second 
Annual Report. This formation includes a lower phosphate bear¬ 
ing member and an upper sand or sandstone member. The lower 
member of the formation contains the workable phosphate de¬ 
posits. The upper member forms the overburden which must be 
removed in mining. 
The phosphate bearing member of this formation is more or 
less definitely stratified, the stratification line being frequently 
continuous along the full length of the pit, a distance of a h^lf 
mile or more. Elsewhere the stratification is irregular and cross 
bedding is evident. 
Although variable from place to place this part of the forma¬ 
tion has an average thickness of from 8 to 12 feet; its maximum 
thickness is possibly 18 or 20 feet. The matrix in which the phos¬ 
phate pebble is imbedded consists largely of clay, sand and soft phos¬ 
phate. The pebble phosphate makes up in the workable deposits 
some ten to twenty-five per cent, of the whole. This member shows 
certain characteristics which are fairly persistent. The lower 2j4 
to 3 feet is usually olive green in color, and contains pebble im¬ 
bedded in clay. The next 3 to 5 feet is frequently dark blue in 
color although oxidizing on exposure to drab or yellow. The up¬ 
per 2 to 4 feet of this member differs much^ particularly in the 
northern part of the area from that which lies below. This upper 
part contains coarser material and has a higher percentage of 
pebble phosphate in proportion to the matrix. The break between 
the coarser material at the top and the more clayey material be¬ 
neath is particularly well marked as seen in the pit of the Coro¬ 
net Phosphate Company in Hillsboro County (PI. 4, Fig 2.) The 
break is here so abrupt as to constitute a distinct unconformity. 
The line of contact is marked by the presence of water worn 
corals, bone fragments and very coarse conglomerate of phosphate 
pebbles. Passing to the south the contact line becomes less marked, 
the conglomerate character of the upper part largely disappearing at 
the south end of the phosphate area. 
The indurated sand above the phosphate has an average thick¬ 
ness of from 10 to 14 feet. Its maximum thickness, however, is 
much greater. On the.other hand owing to decay and erosion these 
sands are in places much reduced and may be locally entirely 
