f geologic data, 409

Panama, manganese, 176

Panama Canal, slides, 416-417

Parker, E. W., and Campbell, M. R., 367, 370-371

Peace Conference, use of geologists in advisory capacity, 356, 406

Peace Treaty, coal and iron situation of western Europe under terms of,
117, 400-403
effect of terms on valuation problems, 335
Silesian lead and zinc ores, 210, 214

Pearls, 289-292

Peat, formation of, 123-124

Pegmatites, 19-20, 35, 39

Peneplains, formation of, 6

Pennsylvania, basalt, 82
clay, 85
coal, 115, 117, 126
flint linings, 269
graphite, 281
iron, 171
limestone, 83
natural gas, 151
petroleum, 133
sand and gravel, 85
sandstone, 84
serpentine, 83
silica for refractories, 195
slate, 85

Persia, petroleum 128-130, 137, 391

Peru, bismuth, 252
borax, 275
coal, 116
copper, 197-198
mercury, 258
molybdenum, 186
nitrates, 103
petroleum, 128, 137
phosphates, 106
silver, 232
tungsten, 183
vanadium, 187, 188

Petroleum, 57, 127-150, 307, 310, 386, 396, 398

Petroliferous provinces, 149, 308

Petrology, relation to economic geology, 3

Philipsburg, Montana, manganese and silver ores, 37, 175, 176-177, 237

Phosphates, 99-100, 104-107, 397

Physiography, general discussion and relations to economic geology, 6-10
_See also_ Topography.

Physiography, relation to bridge building, 413
relation to Hudson River tunnels, 415
relation to railway construction, 418
relation to river and harbor improvements, 414

Pisolites, 172

Pitch. _See_ Asphalt.

Pittman Silver Act, 233

Placers, formation of, 51
gold deposits in, 227
_See also_ Monazite, Platinum, Tin, Tungsten, and other minerals.
use in tracing mineral outcrops, 316-317

Plasticity of clay, 92

Platinum ores, 51, 237-240, 386, 398

Plumbago. _See_ Graphite.

Pogue, Joseph E., 100

Pogue, Joseph E., and Gilbert, Chester G., 119, 134, 138

Poland, lead and zinc, 210, 214

Political and commercial control of mineral resources, 65, 387-388
_See also_ under individual resources.

Porosity of rocks, 69, 141

Porphyry copper ores, 197, 199, 203

Portland cement. See Cement.

Portugal, arsenic, 250
copper, 197-198, 204
pyrite, 107-108
salt, 294
tungsten, 183

Potash, 86, 99-100, 111-114, 386,