Gas springs, 106, 107 Gems, to test by weighing in water, 118 true and false, how to distinguish, 117-124 Glass, minerals which will not scratch, 16, 19 minerals which will scratch, 15, 18 Gold, 46-50 and platinum, washing for, 94, 95 and silver consumed in the arts in the United States, 137, 138 and silver, production of the United States, 137, 138 and silver where they abound, 14 artificial, how made, 125 bearing rock, 88 bearing sands, 88 extraction of, 93 Hill group, silver mines, 136 how distinguished, 89 imitation, how to detect, 125 in California, discovery of, 127-133 in California, first announcement of discovery, 132 in quartz rock, to find the amount of, 98 localities, 46-50 mine first worked in the United States, 133 ore, assay of, 95-98 searching for, 87-89 substances mistaken for, 89 testing any substance supposed to contain, 97 to separate from silver, 97 to test the purity of, 98 where found, 87-89 Granite regions, 14 Graphite, 50, 51 localities, 50, 51 to test the purity of, 104 value, 50 Gravity, mode of determination of, 12 Gray copper ore, 51 localities, 51 value, 51 Gypsum, 14, 52 localities, 52 value, 52 Heavy spar or baryta, 26 Hematite, brown, 56, 57 Horizontal beds, 82 Horn silver, 53 localities, 53 value, 53 Humphrey, Isaac, 128 Indications for minerals, 81 Irish Diamond, 114 Iron, chromic, 34 how it occurs, 94 ore, 14 assay of, 102 bog, 29 brown hematite, 56, 57 lenticular, 56 magnetic, 57, 58 magnetic, found by the compass, 91 micaceous, 62 red hematite, 65, 66 specular, 73, 74 pyrites, 53, 54 localities, 54 value, 53, 54 searching for, 91 spathic, 73 springs, 107, 108 testing minerals for, 91 Jackson, Captain Wm., 133 Jasper, 54 localities, 55 value, 55 Jewelry, artificial, how made and detected, 114-125 Kaolin, 55, 56 localities, 55 value, 55 Lead ore, assay of, 103, 104 to detect silver in, 99 searching for, 90 veins, thickest, 91 where found, 90 Lenticular iron ore, 56 localities, 56 value, 56 Limestone regions, 14 Limonite or brown hematite, 56, 57 localities, 57 value, 57 Magnesian springs, 109, 110 Magnetic, 12 iron ore, 57, 58 found by the compass, 91 localities, 58 value, 58 pyrites, 58, 59 localities, 59 value, 59 Malachite, 59, 60, 101 localities, 59, 60 value, 59 Manganese, oxyd of, 63, 64 spar, 60 localities, 60 value, 60 Marble, 60, 61 localities, 61 regions, 14 Marshall, Jas. W., discovery of gold in California by, 127-131 Metals, found near their source, 82 how they occur, 94 Mica, 61, 62 localities, 62 value, 62 Micaceous iron ore, 62 localities, 62 value, 62 Mineral riches, how discovered, 81 springs, 105-112 location of, 105 no indications of ores, 83 what are they, 105