Excerpt from The Phosphate Deposits of Florida: A Dissertation Lithologic character. - The Vicksburg group includes white \or light colored porous limestones, which are generally soft and crumble So easily that it is difficult to obtain good specimens. On exposure to the air, however, the surface of the limestone hardens as a result of the deposition of calcium carbonate in the outer pores of the rock. Samples obtained in drilling deep wells show that these rocks are remarkably uniform in color and texture to a depth of several hundred feet beneath the surface in the peninsula of Florida. However, the upper part of the limestones of the peninsula include a slight admix ture of land-derived sediments, such as clay and fine sand, and well records indicate that similar conditions exist in western Florida. Layers of light-blue or gray chert, ranging in thickness from a fraction of an inch to several feet, occur in the limestones of this group. Irregular masses and bowlders of flint are found at many places where the rocks belonging to this group are at the surface, and the shells embedded in this flint serve as a valuable guide to determine the areal extent of the rocks of Vicksburg age. Distribution - The limestones of the Vicksburg group underlie all of Florida, but except in small areas in the peninsula and in western Florida they are covered by younger beds of sand, clay, or limestone. In the peninsula the principal area in which these limestones lie at or near the surface extends from a point near Sutherland, Hillsboro County, and Dadc City, Pasco County, northward nearly to Fort White and Lake City Junction, Columbia County. The best expo sures are in Pasco, Sumter, Lake, Citrus, Hernando, Marion, Levy, Lafayette, Alachua, Suwannee, and Columbia counties. Near the margin of the area of the Vicksburg (see map, Pl. 1, in pocket) there are many more or less isolated exposures, the best known being the outliers in Taylor, Jefferson, Columbia, and Suwannee counties. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.