The Railway Children - E. Nesbit

“I've been to my coal-mine,” he said; “to-morrow evening we'll bring home
the black diamonds in the chariot.”
It was a week later that Mrs. Viney remarked to Mother how well this last lot
of coal was holding out.
The children hugged themselves and each other in complicated wriggles of
silent laughter as they listened on the stairs. They had all forgotten by now that
there had ever been any doubt in Peter's mind as to whether coal-mining was
wrong.
But there came a dreadful night when the Station Master put on a pair of old
sand shoes that he had worn at the seaside in his summer holiday, and crept out
very quietly to the yard where the Sodom and Gomorrah heap of coal was, with
the whitewashed line round it. He crept out there, and he waited like a cat by a
mousehole. On the top of the heap something small and dark was scrabbling and
rattling furtively among the coal.
The Station Master concealed himself in the shadow of a brake-van that had a
little tin chimney and was labelled:—