Boat navigation was now nearly at an end. Every day the scouts were sent out in search of roving Indians from whom they might get horses and guides to cross the mountains. But no Indians could be found. A well-beaten trail had been followed high up into the hills, but lost again among defiles so narrow and stony, that when the scouts came back they said no horseman could go through them. So these great mountains, which so long had been to them a guide and landmark, now seemed sternly forbidding their farther progress. Yet at all risks horses and guides must be had. Telling his men he would not come back till he had found them, Captain Lewis set out on his forlorn search, knowing that on him depended the success or failure of the expedition. The men remained encamped where he left them.[2] While engaged in this search, Captain Lewis, on the 12th of August, reached the highest source of the Missouri. At three thousand miles from its mouth it dwindled to a mountain brook. Passing thence over the dividing ridge, he came upon the waters of what proved to be the Columbia. So within a few hours he drank of the waters of both. Following the stream down the mountain, with fresh hope, it led him to a village of the Shoshones or Snake Indians.[3] [Illustration: GATE OF THE ROCKY MOUNTAINS.] No shipwrecked wanderer on an unknown sea ever looked with more eagerness on a rescuing sail than Lewis did upon this uncouth and squalid habitation in the wilderness. The Indians would not believe he had crossed the mountains on foot and without guides. At length, however, some of them agreed to go back with him, and these having found his story true, horses and guides were furnished for the white men's use. Thus equipped, the party began the passage of the mountains, following the obscure windings of a trail known only to the Indians themselves. They found it a hard march. Sometimes it led them through a wild cañon strewed with stones for miles together. Sometimes the caravan would be painfully climbing some slippery height, or skirting the edge of a precipice where a single false step would have flung horse and rider headlong to the bottom of the ravine. But these active little horses, which the Indians rode without saddle or bridle, unshod and ill-fed as they were, did their work to the admiration of the white men. Though they frequently slipped and fell with their burdens, they would quickly scramble to their feet again with the agility of mountain goats.