"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."
"Hist!" exclaimed O'Hara warningly. "I can hear voices."
"It's time for us to go," whispered Armstrong.
Denbigh cast off. The barrel appeared to leap away from them, as the punt was swept down-stream.
"Not much use attempting to land at this point," said Armstrong.
"I don't know so much about that," rejoined Denbigh. "Personally I'm rather anxious to see what these fellows are doing ashore. Keep her going, Pat. We'll strike the bank in less than half a mile."
Paddling in silence the men pursued their tedious course athwart the current until a dull roar was borne to their ears.
"It will be quite ten minutes before it reaches us," replied Denbigh. "Stick to it, lads!"
The amphibians, with the keen instinct that nature bestowed upon them, also were aware of the approach of the foaming mass of water, for the centre of the river was literally alive with hippopotami and saurians that had not gone ashore for a nocturnal ramble. The crocodiles on the mud-flats were either making for deep water or else crawling higher up the banks out of the rush of the irresistible bore.
"Aground!" exclaimed Denbigh as the punt's bows touched the mud. "Check her from swinging round."
Armstrong promptly jumped overboard, to sink above his knees in the soft mud. Only by holding on to the gunwale was he able to keep himself from sinking still deeper.