Suddenly he lurched ahead, his feet sinking in a treacherous mass of sand and gravel. Wildly, he strove to retain his footing, but the effort was in vain. He felt himself slipping and, as he uttered an instinctive cry of warning to Joe, he was flung into space.
Joe, who had been clinging to Frank's coat, was wrenched to one side. He stepped forward, grasping for his brother, then he, too, went hurtling into the darkness.
They pitched down amid a clattering of rocks and pebbles. Then, with an icy shock, they plunged into a deep pool of water!
CHAPTER XIII
The Four Men
Profound darkness enveloped the Hardy boys.
The blackness of the icy pool was no blacker than the darkness of the air above.
Frank rose spluttering to the surface, unharmed by his fall, and as he splashed about, his first thought was for his brother.
"Joe!" he shouted. "Joe!"