THE mineral resources of the United States are of primary importance, for in 1915 that country produced 40 per cent, of the world's output of coal, 40 per cent, of its iron ore, 32 per cent, of its lead and zinc, 60 per cent, of its copper, and 66 per cent, of its petroleum. Since then, some of these proportions have increased. The data for the history of the mineral development of the United States during the War have now been issued in seven thick volumes,1 which contain for each year the full record of the United States output of all important economic minerals, with shorter accounts of the contributions of other countries. The volumes consist mainly of compilations of mineral statistics accompanied by the statement of such geological and economic facts as are necessary to their interpretation. In each volume some chapters, in addition to the annual statistics and record of the year's development, contain a general review of the subject with reference to the current literature and geological descriptions of the chief mining fields. These monographic chapters include those on chromite by J. S. Diller, on graphite, with interesting accounts of its mining in Ceylon and Madagascar, by H. G. Ferguson, on molybdenum by F. L. Hess, on potash by W. B. Hicks, on American utilisation of peat by C. C. Osbon, and on quicksilver by F. L. Ransome. In view of the importance and variety of the American yields, the especially important sections are those dealing with coal, petroleum, and the five metals which are so closely associated that they are recorded together—gold, silver, lead, copper, and zinc.