They had walked on, the semi-circular spot of light at the entrance near the black pipe growing more and more faint, until it was not at all visible.
"There she goes!" exclaimed Dick, looking back.
"What?" asked his brother.
"The last gleam of daylight," was the answer. "If anything happens to our lanterns, so that they go out, and we get mixed up in some branch passages—good night! That's all I have to say!" and Dick was very emphatic in this.
"By Zip Foster!" exclaimed Bud, using that expression for the first time in several days. "You're a cheerful chap to have along on a picnic like this, Dick! Not!"
"Well, might as well prepare for the worst and hope for the best," laughed Dick, while Nort inquired:
"Why don't you tell us more about Zip Foster?"
"Oh—you—say, did you hear anything then?" asked Bud, and his voice had in it such a note of anxiety that his companions did not, at the time, imagine he might have been putting them off from a much-wanted and often-delayed explanation of this mysterious Zip Foster personage.
"Hear what!" asked Dick.
"Something like water running," replied Bud. "I have a notion that our stream—I call it ours for it doesn't seem to belong to anyone else—our stream may just trickle off, now and then, into some other underground course."