“Be careful, boys,” he warned, “a slip here might prove fatal.”
Very cautiously, therefore, they descended into what at first appeared to be a bottomless pit. Suddenly their torches glittered on something that shone like molten metal beneath them.
“Water!” cried the professor.
“A lake,” added Jack, raising his torch so that the light illumined what appeared to be a considerable body of water.
“Water, sure enough,” echoed Pete, “maybe it’s another subterranean river like that one at the Haunted Mesa.”
“This is no river,” said the professor. “See, its surface is as smooth as glass.”
By this time they had descended to the rocky shelf which ran all around the edge of the subterranean lake, while above their torch-light fell redly on a domed roof of dark stone.
“Look! Look!” cried Walter suddenly, “Fish!”
Sure enough, they could now see shoals of white-tinted fish swimming near the surface.