| 1 | This seam of coal reposes on a layer of clay. | |
| 2 | Forests are clear-cut, seams are blasted and massive diggers scoop out the mountain' s coal. | |
| 3 | And PetroChina officials are exploring new shale gas and coal-bed methane opportunities all over the country. | |
| 4 | At "mountaintop removal" mines, which are unique to Appalachian states, miners blast the peaks off mountains to reach coal seams inside and then pile vast quantities of rubble in surrounding valleys. | |
| 5 | The culprit in such cases is usually methane gas, which accumulates in coal beds and can explode when the bed is penetrated during mining. |
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