III. HOUSES OF SAND 21 IV. BRICKS, THEIR FAULTS AND THEIR VIRTUES 31 V. AT THE GOLD DIGGINGS 39 VI. THE STORY OF A SILVER MINE 48 VII. IRON, THE EVERYDAY METAL 57 VIII. OUR GOOD FRIEND COPPER 65 IX. THE NEW METAL, ALUMINUM 76 X. THE OIL IN OUR LAMPS 84 XI. LITTLE GRAINS OF SALT 95 LIST OF ILLUSTRATIONS A STRUCTURAL STEEL APARTMENT BUILDING vi HOW A COAL MINE LOOKS ABOVEGROUND 5 MINERS AND THEIR MINE 10 OPENING A GRANITE QUARRY 13 BUILDING A CONCRETE ROAD 27 IN A NEW JERSEY BRICK MILL 33 HYDRAULIC GOLD MINING 41 THE STORY OF A SPOON 51 IN THE STEEL FOUNDRY 61 IN A COPPER SMELTER 67 A "MOVIE" OF AN ALUMINUM FUNNEL 79 A CALIFORNIA OIL FIELD 87 [Illustration: A STRUCTURAL STEEL APARTMENT BUILDING _Courtesy American Bridge Co._ First the steel frame, then the floors, then the stone or brick shell, then the interior finishing--this is how the building is made.] THE INDUSTRIAL READERS BOOK II DIGGERS IN THE EARTH I IN A COAL MINE Did you ever wonder how beds of coal happened to be in the earth? This is their story.