On the twelfth day of August, an advance party of the explorers crossed the Great Divide of the Rocky Mountains, the birthplace of mighty rivers. Descending the western slope, they found themselves in the country of the Shoshone Indians. Captain Lewis was leading this advance expedition, and, as he neared the highest point of the pass, he realised the significance of the transition from the waters of the Missouri to those of the Columbia. A quotation from his narrative at this most interesting point of the journey gives the reader a better conception than any description could, of the feelings of the explorers: The road was still plain, and as it led directly toward the mountains, the stream gradually became smaller, till after their advancing two miles further, it had so greatly diminished in width that one of the men in a fit of enthusiasm, with one foot on each side of the rivulet, thanked God that he had lived to bestride the Missouri. As they proceeded, their hope of seeing the waters of the Columbia rose to almost painful anxiety; when at the distance of four miles from the last abrupt turn of the stream, they reached a small gap formed by the high mountains which recede on either side, leaving room for the Indian road. From the foot of one of the lowest of these mountains, which arises with a gentle ascent of about half a mile, issued the remotest water of the Missouri. They had now reached the hidden sources of that river, which had never before been seen by civilised man; and as they quenched their thirst at the chaste and icy fountain,--as they sat down by the brink of that little rivulet, which yielded its distant and modest tribute to the parent ocean,--they felt themselves rewarded for all their labours and difficulties. They left reluctantly this interesting spot, and pursuing the Indian road through the interval of the hills, arrived at the top of a ridge from which they saw high mountains, partially covered with snow, still to the west of them. The ridge on which they stood formed the dividing line between the waters of the Atlantic and the Pacific Oceans. They found the descent much steeper than on the eastern side, and at the distance of three-quarters of a mile, reached a handsome, bold creek of cold, clear water running to the westward. They stopped to taste for the first time the waters of the Columbia. The party was now upon the western slope of the Great Divide, in the vicinity of the present Fort Lemhi in Eastern Idaho. They supposed that they were almost to the Pacific, not realising that a thousand miles of difficult and dangerous travel and more than two months of time still separated them from their wished-for goal. The journey, in fact, from the springs of the Missouri to the navigable waters of the Columbia, proved to be the most critical of the whole series.