rces, 65, 387, 388
_See also_ under individual resources.

Common rocks, as mineral resources, 80-94

Comstock Lode, Nevada, silver ores, 235-236, 308

Congo. See Belgian Congo

Connecticut, basalt, 82
diatomaceous earth, 269
tourmaline, 293

Conover, Julian D., 12

Conservation, 359-382, 393-395
application of economic geology to, 1-2
of coal, 366-382
of common rocks, 81
of human energy, 362
international aspects, 362-363, 375, 376-377, 393-395
of petroleum, 137-139

Conservation Commission of Canada, 367

Contact metamorphism, 20, 24, 25-27, 36-37
_See also_ Igneous after-effects.

Contracts, classification of earth materials in, 356-357

Copper ores, 9, 36-50, 51-52, 55, 197, 209, 307, 308-309, 313-314, 318,
396

Cornwall, England, tin ores, 42, 260, 262, 263
uranium and radium ores, 264

Corocoro, Bolivia, copper ores, 206

Corundum, 267-268, 270, 398

Costa Rica, manganese, 176

"Cracking" processes for refining petroleum, 137, 139

Cripple Creek district, Colorado, gold ores, 230

Cuba, chromite, 179
copper, 197
iron, 8-9, 50, 58, 96, 155, 160, 163, 171-173, 313, 349
manganese, 175
nickel, 181
petroleum, 128

Cuyuna Range, Minnesota, manganese ores, 175, 177

Cycle, erosion or topographic, 6-7

Cyclic nature of ore concentration, 7-8, 47-48, 56, 169, 201, 205, 208,
325

Cyprus, asbestos, 271, 272

Dams, geologic problems involved in construction, 414

Davis, W. M., 408

Death Valley, California, borax deposits, 276

Degree of economic geology, 427-428

Denmark, cement, 87
chalk, 83
grinding pebbles, 268

Depletion of mineral deposits, as factor in valuation and taxation,
331, 337, 339

Depth as a factor in mineral deposition, 43, 49, 58-59

Diamond dust, 267, 268, 398

Diamonds, 289-292, 316, 317

Diatomaceous earth, 267, 269, 398

Diorite, 82

Dolomite, 23, 192

Domes, occurrence of oil in. _See_ Anticlines.

Domes, salt and sulphur, Gulf Coast, 110, 298

Drilling, exploration of mineral deposits by, 320-321

Drilling records, public registration of, 305-306

Ducktown, Tennessee, copper ores, 204

Dutch East Indies, natural gas, 151
petroleum, 128, 129
tin, 260
use of coefficient to estimate tin reserves, 322

Dutch Guiana, bauxite, 243

Dutch West Ind