Economist: WITH a metallic gasp, the chute opens its metal jaws and deposits precisely 230,000 pounds of coal into the railway car. The pour is carefully calibrated to create an aerodynamically efficient heap; sealant is sprayed evenly across the coals surface to limit dust release. Fully loaded, the car moves along to be replaced by another; it takes two-and-a-half hours to load the two-mile-long train. Four trains, each carrying 15,000 tonnes of coal, leave the Spring Creek mine in Montana every day, often...