In phosphate pits of the Bone Valley district of Florida three different kinds of materials generally are exposed--Hawthorne bedrock or bed-clay of Miocene age, overlying concentrations of phosphorite of Miocene and Pliocene ages, and a surface blanket of loose to slightly indurated quartz sand. The current concept that the surface sand blanket is an insoluble residue developed in situ through weathering, and as a consequence of this origin reflects the environments in which the underlying phosphorites accumulated, is concluded to be incorrect. This result is based on studies and comparisons of grain size analyses of quartz sand, on heavy mineral data and on fossil evidences.

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