First is considered the question of petroleum, source of power and light, the key to the mastery of the air, and, on account of its fluid and easily transportable condition, of extraordinary future importance. Next are taken up the great fuel mineral, coal, and its ally, the great metallic mineral, iron, which must go together for the manufacture of iron and steel, the backbone of all our mechanical achievements. Next come those metals indispensable in steel making and in the manufacture of specially hard or tough steels. These are of great importance, and include manganese, chromium, nickel, tungsten, vanadium, antimony, molybdenum, uranium, and zirconium. Radium is closely associated with uranium and is considered with it. Closely allied with zirconium are thorium and mesothorium, and their treatment therefore closely follows that of zirconium. The next great group is that of the major metals, other than iron and the ferro-alloy metals: copper, lead, zinc, tin and mercury, and aluminum. Aluminum ores are used not only as sources of the metal, but for the manufacture of refractories and abrasives. Therefore they are classed partly with the metallic and partly with the non-metallic minerals; and the other non-metallic minerals, used likewise for abrasives, refractories, and other uses--such minerals as emery and corundum, magnesite, graphite, mica, and asbestos--follow. The next great group is that of the fertilizer minerals--phosphate rock, potash, nitrates and nitrogen, and pyrite and sulphur, all essential for agriculture. The last group is that of the precious metals, gold, silver, and platinum, essential for coinage and in the arts. These various studies are essentially both inclusive and elementary: together they form almost the first contribution to the branch of investigation--that of the relation of geology to industry, commerce, and political economy--which they cover; and it is natural that beginnings should be rather crude. Moreover, many of the chapters were written a year or more previous to the publication of the volume, and although brought to date to the extent possible in the brief time available, are considered inadequate by the authors themselves. Apologies for shortcomings and possible inaccuracies are therefore very much in order. Nevertheless, it is felt that the volume merits publication, and that the beginning here made is far better than no start at all. JOSIAH EDWARD SPURR. CONTENTS PAGE PREFACE v CHAPTER I. PETROLEUM, BY JOHN D. NORTHROP 1 II. COAL, BY GEORGE S. RICE AND FRANK F. GROUT 22 III. IRON, BY E. C. HARDER AND F. T. EDDINGFIELD 55 IV. MANGANESE, BY D. F. HEWETT 90 V. CHROMIUM, BY E. C. HARDER 109