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<br />. <br /> <br />. <br /> <br />. <br /> <br />oon2:9 <br /> <br />CHAPTER VI <br /> <br />MINERAL'3 <br /> <br />Coal <br /> <br />Bituminous coal deposits are found in the Dakota sandstone of Cre- <br />taceous age in the San Juan Area. The coal is in the middle shaly member <br />of the Dakota where the seams are short, discontinuous, and thin, ranging <br />up to 3 feet in thickness. The coal is normally high in ash and weathers <br />into small fragments and fine powder. <br /> <br />Only a few coal mines have been opened in the area. All were small <br />and have been abandoned. Development has been discouraged by the high <br />ash content, the thin, discontinuous seams, and the poor market area. A <br />thicker deposit of higher ~uality bituminous coal is reported to have <br />been encountered near the surface in the eastern part of San Juan County <br />in the course of exploratory drilling for other minerals. The extent and <br />significance of the deposit have not yet been appraised. <br /> <br />Miscellaneous Minerals <br /> <br />Other types of mineral deposits found in the San Juan study area in- <br />clude clay, construction materials, dimension stone, gold, silver, gypsum, <br />iron, limestone, and semiprecious stones. Except for construction mate- <br />rials, the impact of these minerals upon the economy of the region has <br />been slight, some of them never having achieved production. Because of <br />such factors as distance to market, small size of the deposits, 'or low <br />value per ton, many may not be developed within the foreseeable future. <br />The production of construction materials for local use will increase <br />and become progressively more important as the population of the region <br />increases. <br /> <br />64 <br />