"Hulloa, what's that?" whispered the Irishman. "Hippos right across the river."
The punt was bearing down upon a line of dark objects that were apparently forging ahead against the swift current.
"Back starboard!" ordered Denbigh promptly.
The punt, checked by the resistance of O'Hara's palms in the water, swung sideways. As it did so Denbigh gathered up the slack of the severed lead-line that still remained on board.
Retaining the ends he threw the bight across one of the black objects, at the same time lying at full length on the bottom of the boat. With a jerk that wellnigh capsized the crank craft the punt's way was checked.
"Your hippos are barrels, old man!" he exclaimed.
"Mines, perhaps," suggested Armstrong. "Be careful, for goodness sake."
"Not mines," declared Denbigh. "They wouldn't be floating on the surface. But it's some infernal contrivance. Haul closer and we'll investigate."
Warding off the gunwale from the plunging barrel Denbigh dipped his arm into the water. His hand came in contact with a heavy chain eighteen inches beneath the surface.
"A boom!" he announced. "By Jove! If we had a slab of gun-cotton handy."