Derrick felt deeply thankful that his life had been thus preserved, as he walked thoughtfully beside the mine boss away from the scene of disaster. "How invariably Nature asserts herself in the end, and defies the puny efforts of man to alter her ways," said Mr. Jones to himself, musingly. Then to his companion he said, "I brought you with me to try you, Derrick. I hated to come myself, for I did not know what might be going on, after all these squeezes and movements of the mine. It had to be done, though, and it seemed a good opportunity for testing your courage, so I asked you to come with me. As a mining engineer, you will often be called upon to perform similar unpleasant and dangerous tasks." "I was afraid, and didn't want to come one bit," said Derrick, with a nervous laugh. "That doesn't make any difference. I was afraid too, but we came all the same. The proof of your courage is not whether you are afraid to do a thing or not, but whether or not you do it." So Derrick's courage was tested, and withstood the test, which was indeed fortunate; for, within a short time, he was to be placed in a position that would try the courage of the bravest man in the world. CHAPTER XVI BURSTING OF AN UNDERGROUND RESERVOIR Upon reaching the surface that evening, Derrick and the mine boss found that the weather had greatly changed since noon and that a storm threatened. It set in that night, and the rain poured down in a steady, determined sort of way, as though it had made up its mind that this time, at least, the earth should be thoroughly watered. When Derrick joined the other miners at the mouth of the slope in the morning, it was still raining, and as they were lowered into the underground world, the men joked with each other about getting in out of the wet, and pitied the poor fellows who were obliged to work above-ground on such a day. Descending the second slope into the lowest level of the mine, Tom Evert and his party made an examination of the place in which they were to work. The new excavations on this level were of limited extent, work having only recently been begun on them; but a powerful pump had been placed at the top of the slope leading down into them, and it was to bring the accumulated water in the old workings within reach of it that the mine boss had sent them down. Going up the old gangway, past the chamber at the foot of the air-shaft which Derrick had such good reason to remember, they soon came to the fallen mass of rock, coal, and earth through which they were to cut a channel and insert a pipe for the release of the water beyond. The material was too loose for blasting, so the work had to be done with pick and shovel, and the debris removed with wheel-barrows, and distributed along the gangway. It was hard, dangerous, and exhausting work, and at the end of three days Derrick was heartily tired of it.