The silhouettes

Gerelateerde afbeelding

On both sides of the interstate, above the silhouettes of screening trees, we saw the tops of draglines-the necks and heads of industrial giraffes. They and predecessor machines had been working for fifty years, altering the topography, stripping the coal beds of Pennsylvania-in all, a mineral deposit worth a great deal more than the diamond mines of Kimberley and the goldfields of the Klondike. Coal was in the roadcuts now and would continue to be for many tens of miles-in layers that were not the dull deep gray of the Allegheny shale but truly black and shining. Layered light and dark, the roadcuts looked like Hungarian tortes. Reading up from the bottom, there was sandstone, siltstone, shale, coal, sandstone, siltstone, shale, coal. We would see limestones farther on, capping the coal where sea had covered the swamps. The present sequence was built behind a coastline-as is happening now, for co-working space rotterdam example, in the bayous of the Mississippi Delta-by rivers meandering to and fro, covering with sand the matted vegetation. “These roadcuts are a textbook on the making of coal,” Anita said. Buried and compressed, vegetal debris first becomes peat-a melange of spores, seed coats, wood, bark, leaves, and roots which looks like chewing tobacco and burns about as well. Peat bears much the same relation to coal that snow does to glacier ice. As snow is ever more buried and compacter!, it recrystallizes and becomes ice-on the average ten times as dense as the original snow. As peat is buried, compacted, subjected to geothermal heat, it gradually gives up much of its oxygen, hydrogen, and nitrogen, and concentrates its content of carbon. The American co-working space amsterdam Geological Institute’s Glossary of Geology defines coal as “a readily combustible rock.” By weight, any rock that is half carbonaceous material is coal. Its density is roughly ten times the density of peat. In the United States, there is enough peat to keep Ireland warm for a thousand years. The United States uses almost none of it, because the United States also happens to have a great deal more coal than any other country in the world. Peat that remains near the surfa ce will never become coal. Buried three-quarters of a mile, it becomes bituminous.

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