Both Mrs. Halford and Miss Nellie were greatly interested in watching the machinery of the breaker and the quick work of the slate-picker boys; but in spite of the jigs and the wet chutes the coal-dust was so thick that they did not feel able to remain there more than a few minutes.
As they came out Mrs. Halford said, "Poor little fellows! What a terribly hard life they must lead!"
"Yes, Mamma, it's awful," said Miss Nellie. "And don't they look just like little negro minstrels? I don't see, though, how they ever tell the slate from the coal. It all looks exactly alike to me."
"The slate isn't so black as the coal," explained Derrick, "and doesn't have the same shine."
They walked out over the great dump, and the ladies were amazed at its extent.
"Why, it seems as if every bit of slate, and coal too, ever dug in the mine must be piled up here!" exclaimed Miss Nellie.
"Oh no," said Derrick, "only about half the product of the mine is waste, and only part of that comes up here. A great quantity is dumped into the old breasts down in the workings to fill them up, and at the same time to get rid of it easily."
"But isn't there a great deal of coal that would burn in this mountain of refuse?" asked the girl.
"Yes, indeed, there is; and sometimes the piles get on fire, and then they seem to burn forever."
"I have an acquaintance in Philadelphia," said Mrs. Halford, "who has been trying experiments with the dust of these waste heaps. He pressed it in egg-shaped moulds, and has succeeded in making capital stove coal from it. The process is at present too expensive to be profitable, but I have no doubt that cheaper methods will be discovered, and that within a few years these culm piles will become valuable."