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Introduction. ____________________ _ _______________ Acknowledgments __ ___________ _ _________________ What is "black shale"? ____________________ What is "uraniferous black shale"? __ _______________ Historical review of investigations for uraniferous black shales. ______________________________ _ _________ Investigations, 1944-47 _ _______________________ Investigations, 1947-52 _ ______ _ __________ _ _ Investigations, 1952-57 _ _______________________ Summary.-._ __________________________________ Sources of uranium and mechanisms of its enrichment. __ Examples of uranium-bearing shale and mud_______ Sources _ _____________________________________ Sources and chemical form of uranium in sea water. __________________________________ Uranium content of modern sea water_________ Uranium content of water in ancient seas______ Influence of source rock on uranium content of water in bordering seas______-_-____-____ Mechanisms of enrichment _ ________________ _ __ Organic matter.... _________________________ Amounts and types in uranium-bearing shale and mud_ ____ ______ _ Solid organic matter________________ __ Humic acids. __________________________ Uranium incorporated by living plants or animals __ _________________________ Hydrogen sulfide __________________ ______ Precipitation of uranium __ _____________

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C.1TUS L " ^ ^ ^^^^ ^ ^ JLJL 3. Percent of samples by coal rank 16 4. Average composition of all coal samples in United States and of ranks of coal 17 5. Means and ranges of analyses, 53 anthracite samples, Pennsylvania anthracite region 25 6. Sample descriptions and analyses, 53 anthracite samples, Pennsylvania anthracite region 28 7. Means and ranges of analyses, 331 coal samples,