GEOLOGIC SETTING AND CHEMICAL COMPOSITION OF PIERRE SHALE Scandium, vanadium, and gallium, and possibly chromium and copper, are likely to occur in larger amounts in a zone in the lower part of the Pierre than in a middle zone of the Pierre. The middle zone contains larger amounts of calcium and manganese than the lower zone, and nickel, strontium, and possibly yttrium, are likely to be present in larger amounts in the middle zone. Calcium, manganese, and strontium are present in larger amounts in samples from the eastern part of the area than from the western, and boron and nickel seem to be distributed similarly. Scandium and lanthanum seem to be present in larger amounts in samples from the western part of the area. The plastic and liquid limits measured for samples of the Pierre are characteristic of clays of mixed mineral composition. The figures for the liquid limit seem to be directly proportional to the amount of montmorillonite in the samples, to the pH produced by the sample, and to the amount of material finer than about 4 microns in the sample. No regularities could be made out between the plastic limit and other characteristics of the samples. DISTRIBUTION OF PIERRE SHALE AND EQUIVALENT ROCKS the shore, and in terrestrial environments extending from behind the shore to near the source areas that furnished the sediments. 3. Southern Wyoming, Colorado, and parts of New Mexico and Utah. The study in this area will provide additional data on changes in chemical and mineralogic composition of shale and associated rocks from locations in terrestrial and near-shore environments near source areas on the west and in marine environments near the center of the basin of the Pierre sea. ACKNOWLEDGMENTS Mr. A. H. Burling, project geologist, Oahe Unit, U.S. Army Corps of Engineers, Pierre, S. Dak., provided information on the stratigraphic subdivisions of the Pierre shale in excavations and core holes at the Oahe Dam. Dr. E. P. Rothrock, formerly State geologist of South Dakota, provided much information on the distribution of the Pierre shale in South Dakota and other assistance. Dr. A. F. Agnew, present State geologist of South Dakota, also extended many helpful courtesies. Important contributions were made by a steering committee consisting of W. W. Eubey, W. S. Burbank, D. J. Varnes, and E. M. Shoemaker of the U.S. Geological Survey and M. N. Bramlette, Scripps Institution of Oceanography, La Jolla, Calif., both in planning the investigations and interpreting the results. All analyses were made in the laboratories of the U.S. Geological Survey, Denver, Colo. L. B. Eiley, Lee C. Peck, A. Tennyson Myers, and L. F. Eader, Jr., have assisted in planning the analytical work and aided in the interpretations of analyses. W. A. Cobban has identified the collections of fossils and has generously made available his knowledge of the stratigraphy and paleontology of Upper Cretaceous rocks of the western interior region. J. R. Gill and L. G. Schultz, who are participating in the subsequent investigations of the Pierre shale...