Progress was in consequence tediously slow, an hour elapsing before the boat joined the wider expanse above the defile. Ahead the river broadened still more into a fairly large lake which the map had entirely ignored. At the farthermost end the flat shores were broken by a number of rocky pinnacles, but whether they were small islands or merely parts of the mainland, it was as yet impossible to determine. The forests had now been left behind, the shores of the lake being treeless and bare, save for occasional patches of pampas grass and cacti.
"Think we'll fetch the other end before dark, Uncle?" asked Peter. "It's quite five miles off."
"Might," replied Brian unconcernedly. "It doesn't matter much if we don't. We're carrying on at night. I think we decided upon that?"
"Yes," agreed his nephew, "we did. But we didn't reckon on having to navigate a lake. We don't know where the inlet is. It might be between any of those projections we can see ahead; and it will be no joke barging about on a dark night trying to find a way out."
"We'll do it, never you fear," rejoined his uncle, with one of those bursts of sublime optimism that characterized his mercurial spirits.
Soon it became evident that Peter had miscalculated the length of the lake. Darkness was drawing nigh and still the range of rocky pinnacles was far enough away to baffle any attempt to fix the channel with any degree of reliability.
The wind, too, hitherto light, was piping up dead astern and against the slight but distinctly perceptible current.
Peter was steering. More than once he glanced astern at the curling waves. In a craft possessing any degree of seaworthiness he would not have troubled to look behind him, knowing the short-crested waves would pass harmlessly under the boat's keel. But the keelless type of freak construction was already giving signs of trouble. The metal rudder, of absurdly insignificant proportions, had little or no grip, except when at short intervals the narrow stern, weighted by the heavy outboard engine, dipped dangerously in the hollow water. At one moment the engine was almost stopped by the increased resistance of the deeply immersed blades; at another, the motor was racing furiously as the "orange-box" buried her bows and threatened to broach-to.
Both men realized the danger. Wave-crests were flicking over the sides of the little craft. Brian Strong was busily engaged in baling. Peter was endeavouring to keep the boat on her course, the while striving to discern an outlet between the still distant rocks.
Presently darkness fell upon the scene. The wind was increasing and now blew with the force of a "fresh breeze". Peter would have laughed at it in a seaworthy centre-board dinghy, but in present conditions, he knew it was far from being a laughing matter. Somewhere, and not very far distant by this time, was a lee shore. The "rebound" from the land at this end of the lake was already becoming apparent, for the waves were now becoming irregular and confused. Uncle Brian's task was a difficult one, for of all sorts of craft those with flat bottoms are the most awkward to bale out. In spite of his strenuous efforts the water was gaining. He communicated the news to his nephew.