22 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
chemical activity within the formation itself. Although exceedingly variable from place to place 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.
The 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 phosphate associated with the sands is variable. They are also more or less -calcareous in places. 'Upon prolonged exposure, as seen inl 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 they become reddish or ochre-yellow in color.
The clays in this formation occur locally as clay lenses imbedded 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 of clay in' the phosphate-bearing formation increases in a general way in passing to the south. The exposures in the southern part of the area show as a rule more clay than do similar exposures in the northern part of the area.
Flint boulders occur locally in this formation in some abundance, and occasionally phosphate pits which are otherwise workable are abandoned on account of the number of flint boulderS, encountered. The flint boulders are usually oval or somewhat flattened in shape and are of varying size, some weighing several tons. The exterior is usually of a light color. Some of the boulders are' hollowv and' are occasionally filled with water. Others are solid, compact and of a bluish color throughout. Fossils or casts of fossils occur frequently within the boulders. Limestone inclusions-, f rom the underlying f formations are f requent in this f orm-ation.
The pebble conglomerate feature is not of frequent occurrence but may occasionally be observed in the northern part of the