310 THE ELEMENTS OF ECONOMIC GEOLOGY

Mercury, ores of, 119-2 5; Almaden,
120-1; association of ores with
Kainozoic mountain movements,
123-5; California, 123; China,
123 ; Idria, 121-3; price, 120;
qualities, 119; in sinters, 21.
Metal, definition of, 3; source of,
7.
Micas, 157-60 ; age, 157 ; distribution
 and uses, 15% ; mining econo:
mics, 159-60; phlogopite, 158
Pneumatolytic origin, 1 57; price,
160.
Mineral, definition of and mineral
species, 2-3.
Mineral fuels, 259-96,
Mineral oil, 274-96.
Monazite, 161,
Moss mining, 39.
Mother lode of California, 38,
Mud volcanoes and oil, 281,
Mulch, effect of, 195.
Mullock, 12.

NEPHRITE, 166.
Nickel, price and uses, 113. Ores
of, 113-9; Africa, South, 119;
Gap Mine, 118; New Caledonia,
118; of S.W. Scotland, 119;
Sudbury Field—genesis of the
ores, 114-8,
Nitrates, 197-200; formation,
theories of, 198-9 ; reserves, estimates
 of, 199-200.
Nugget formation, 29-40. 69.

Oi, 274-96; age of, 278; anti
clinal theory founded by Sterry
Hunt, 284; Baumé scale, 276
bitumen veins, 280; brea, 280,
282, 289; indications of, 280-3 ;
isovols, 281 ; mud volcanoes and,
281; origin of, 278-80 ; petro
leum, 274-94; pitch lakes, 280,
290; pyrobitumen, 294; re
sources, estimation of, 285-6;
supply of, 276-7.
Dilfields, essential structures, 283
Appalachian, 286-7 ; Argentine,
292; Burma, 293; Californian,
288; Canadian, 290; Caucasus,
293 ; Eastern Archipelago, 294 :

European, 292-3 ; Mexican, 289 ;
Mid Continental, U.S.A., 287;
Persia and Mesopotamia, 293 ;
Peruvian, 29; Rocky Mountain
288; South American, 291;
West Indian, 290-1.
Oil-pools, 292-3,
Oil shale, 294-6 ; Scottish, 29.
Olivine, 167.
Opal, 167.
Ore, definition of, 3; formation of,
14-16; formation, 27-9; depth of,
see Depth. Ore formation in
relation to igneous rocks, 17-19.
Ore-grade, 3; history and study
of, 14-16; igneous, 26; magmatic,
 23-6; microscopic study
of, 32; sequence in depth, 20-2,
27-30; sporadic distribution of, 4.
Ore-zone, the, 17-20.
PANAMA breaks, 179,
Peat, 261.
Pegmatites and ores, 23, 44, 77, 166.
Percolation wells, 229.
Peridote, 167,
Petroleum, 274-94; history and
nature, 274; physical classification,
 275.
Phosphates, 32-3, 200-5; apatite,
200-1; coprolites, 203; forma:
tion of phosphates, 201; granular
 phosphates, 204 ; guano,
201-3 ; lagoon phosphate, 203;
phosphatic chalk, 204 ; phosphatized
 volcanic rock, 203; rock
phosphate, 202; staffelite, 203 ;
supply of, 205; value and use of,
200.
Placers, 32, 37, 53, 63-4, 147.
Pipe lodes, 9, 64, 81, 83, 83.
Pitch lakes, 280, 290.
Platinum, price and qualities, 65.
Ores of, 65-70; age of, 69 ;
British Columbia, in, 68 ; Africa,
South, 67; Russia, 66-7; distribution,
 65; genesis, 68-70.
Pneumatolysis, 26, 36, 37, 41, 43-4,
71, 73, 76, 77, 79, 81, 82-3, 97,
162, 164, 166, 169-73.
Potash salts, 214-7; derivation
from sea-water, 214: distribu-