Bearing a dark lantern, he took the lead and Richard followed.

About twenty rods up the drain, Inspector Val stumbled and all but pitched upon his face.
"Look out!" he cried, by way of warning.
The next moment Richard set his foot on something soft and yielding, which exploded with a great noise.
"One of those rubber propositions," explained Inspector Val.
By the light of the lamp, and as far up the drain as his eye would reach, Richard beheld a seemingly endless file of circular rubber air-cushions, mates of the one Inspector Val had brought him.

On the six-inch depth of water which raced along the cushions were floating light as corks; in the center of each reposed a canvas sack of gold.

As Steamboat Dan explained, this long line of argosies had been brought to a standstill by laying an iron bar across so as to detain the little rubber-rafts while the stream ran on.

Inspector Val had tripped over this bar.