"June 3, 1805.--We came to for the night, for the purpose of examining in the morning a large river which enters opposite to us. It now became an interesting question, which of those two streams is what the Indians call Ahmateahza, or the Missouri, which, they tell us, has its head waters very near to the Columbia. On our right decision much of the fate of the expedition depends; since, if, after ascending to the Rocky Mountains or beyond them, we should find that the river we have been tracing does not come near the Columbia, and be obliged to turn back, we shall have lost the travelling season, and seriously disheartened our men. We determined, therefore, to examine well before deciding on our course, and, for this purpose, despatched two canoes with three men up each of the streams, with orders to ascertain the width, depth, and rapidity of the currents, so as to judge of their comparative bodies of water. Parties were also sent out by land to penetrate the country, and discover from the rising grounds, if possible, the distant bearings of the two rivers. While they were gone, the two commanders ascended together the high grounds in the fork of the two rivers, whence they had an extensive prospect of the surrounding country. On every side, it was spread into one vast plain covered with verdure, in which innumerable herds of buffaloes were roaming, attended by their enemies the wolves. Some flocks of elk also were seen; and the solitary antelopes were scattered, with their young, over the plain. The direction of the rivers could not be long distinguished, as they were soon lost in the extent of the plain. "On our return, we continued our examination. The width of the north branch is two hundred yards; that of the south is three hundred and seventy-two. The north, though narrower, is deeper than the south: its waters also are of the same whitish-brown color, thickness, and turbidness as the Missouri. They run in the same boiling and roaring manner which has uniformly characterized the Missouri; and its bed is composed of some gravel, but principally mud. The south fork is broader, and its waters are perfectly transparent. The current is rapid, but the surface smooth and unruffled; and its bed is composed of round and flat smooth stones, like those of rivers issuing from a mountainous country. "In the evening, the exploring parties returned, after ascending the rivers in canoes for some distance, then continuing on foot, just leaving themselves time to return by night. Their accounts were far from deciding the important question of our future route; and we therefore determined each of us to ascend one of the rivers during a day and a half's march, or farther, if necessary for our satisfaction.