Parts of the teeth include: 1  Enamel: The hardest, white outer part of the tooth. Enamel is mostly made of calcium phosphate, a rock-hard mineral. 2  Dentine: A layer underlying the enamel. Dentine is made of living cells, which secrete a hard mineral substance.  Pulp: The softer, living inner structure of teeth.
Though they vary significantly, transportation costs accounted for 40% of the average overall cost of coal delivered at electric power plants in 2010. On average, nominal U.S. rail rates for shipping coal grew from $11.83 to $17.25 per short ton from 2001 to 2010.
Between 1810 and 1819, the average cost of .30 per ton-mile prohibited the long distance movement of goods. More specifically, in 1817, New York found the cost of transportation from Buffalo to New York City was three times the market value of wheat, six times of corn, and twelve times of oats.