The Encyclopedia Americana, Količine 1–30Bernard S. Cayne Grolier, 1981 |
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Stran 137
Bernard S. Cayne. COAL : 4. Coal Mining and Production COAL MINING PROCEDURES COAL : 4. Coal Mining and Production TAL : 4. RECOVERABLE COAL RESOURCES ( Mapped and explored ) Percent of world total In billion metric tons Soviet Union ...
Bernard S. Cayne. COAL : 4. Coal Mining and Production COAL MINING PROCEDURES COAL : 4. Coal Mining and Production TAL : 4. RECOVERABLE COAL RESOURCES ( Mapped and explored ) Percent of world total In billion metric tons Soviet Union ...
Stran 139
... mined and the roof allowed to cove as the miners proceed . The British bord - and - piliar need is a variation of these nebud SMALE ACMANDING SEAM WORKING BACE LONGMALL RETREATING ROON - AND - PILLAR MINING TECHNIQUE GALLERIES Ing - wall ...
... mined and the roof allowed to cove as the miners proceed . The British bord - and - piliar need is a variation of these nebud SMALE ACMANDING SEAM WORKING BACE LONGMALL RETREATING ROON - AND - PILLAR MINING TECHNIQUE GALLERIES Ing - wall ...
Stran 629
... mines are literally " mined out " ; rather , they close because the cost of operation comes to exceed the value of the minerals produced . It is this characteristic that has led to " ghost " mining towns such as Virginia City , Nev ...
... mines are literally " mined out " ; rather , they close because the cost of operation comes to exceed the value of the minerals produced . It is this characteristic that has led to " ghost " mining towns such as Virginia City , Nev ...
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