Nickel ores, 34-35, 180-182, 307, 308, 318, 398

Nitrates, 99-100, 101-104, 386, 392, 398

Nonesuch beds, Michigan, copper ores, 52, 206

North Africa,
iron, 156, 160, 161, 164
lead, 210
phosphates, 104, 105, 106
potash, 112
zinc, 214-215

North Carolina,
coal, 117
corundum, 268, 270
emeralds, 293
feldspar, 86
garnet, 268
granite, 82
mica, 287
monazite, 288, 289
rubies, 292
sand and gravel, 85
sapphires, 293

Northern Plains, coal, 118

Norway,
copper, 197-198
molybdenum, 186
nickel, 180
titanium, 190
zinc, 214
_See also_ Scandinavia.

Nova Scotia,
gypsum, 283-284
saddle-reef gold ores, 41

Oceania,
mercury, 258
phosphates, 105, 106
tin, 261

Ohio,
bromine, 277
clay, 85
coal, 117
grindstones and pulpstones, 269
gypsum, 284
hones, oilstones and whetstones, 269
limestone, 83
natural gas, 151
petroleum, 133
salt, 294
sand and gravel, 85
sandstone, 84

Oil. _See_ Petroleum.

Oil shales, 56, 139, 150-151

Oilstones, 269

Oklahoma,
asphalt, and bitumen, 152
gypsum, 284
lead, 211
natural gas, 151
petroleum, 132, 133, 135
tripoli and rottenstone, 269
zinc, 215

Ontario, Canada,
arsenic, 251
cobalt, 255
corundum, 270
mica, 286
nickel, 34-35, 180-182, 308, 312, 318
platinum, 238, 239
silver, 232, 234-235, 308, 316
talc, 299, 300

Ontario, Canada, laws relating to ownership of mineral resources, 344

Onyx marble, 83

Open-hearth process of steel making, 158-159

Ore deposits. _See_ Mineral deposits.

Oregon, borax, 275, 276
chromite, 179
mercury, 257

Origin of mineral deposits, as a factor in economic problems, 29-31,
322-323

Outcrops of mineral deposits, 311-316

Ownership laws, effect on exploration of mineral deposits, 347-349
relation of geology to, 349-355

Oxide zones, 22, 46-50, 313-314
_See also_ under Copper ores, Silver ores, etc.

Pablo Beach, Florida, titanium ores, 190-191
zirconium ores, 189

Pacific coast, possible establishment of iron and steel industry, 155,
165

Pacific coast province, coal, 117

Palegeography, relation to economic geology, 4

Paleontology, relation to economic geology, 4

Palestine campaign, use o