Towards the middle of June the fall of the rivers showed that the great body of snow on the mountains was at last melted; and they ventured to leave their encampment, against the advice of several of the Indians. They, however, soon found that they had been premature in their motions; for, on the higher grounds, there was no appearance whatever of vegetation. The snow, which covered the whole country, was indeed sufficiently hard to bear the horses, but it was still ten or twelve feet deep; so that a further prosecution of their journey was, at present, impossible; and the travellers, after having deposited, in this upper region, their baggage, and such provisions as they could spare, reluctantly traced back their steps to the plain. There they remained ten days; and, on the 26th, they again began to ascend the lofty ridge; the snow on which had, in the interval, melted nearly four feet, leaving still a depth of six or seven. They now implicitly followed the steps of their guides, who traversed this trackless region with a kind of instinctive sagacity: these men never hesitated respecting the path, and were never embarrassed. In three days they once more reached the stream which, in their former journey, they had named _Traveller's Rest Creek_. Here Captains Lewis and Clarke agreed to separate, for the purpose of taking a more comprehensive survey of the country in their journey homeward. It was considered desirable to acquire a further knowledge of the Yellow-stone, a large river which flows from the south-west, more than one thousand miles before it reaches the Missouri; and it was of importance to ascertain, more accurately than they had hitherto done, the course of Maria's river. The separation took place on the 3d of July; and Captain Lewis, holding on an eastern course, crossed a large stream which flowed towards the Columbia, and which had already been named _Clarke's river_. On the 18th of July he came to _Maria's river_, the object of his search; and he continued for several days, his route along its northern bank. After having ascertained the course of this river, he again set out on his journey homeward, that he might not lose the opportunity of returning before the winter. He and his companions were only four in number; and, in one part of their journey, they had an alarming intercourse with a party of Indians. Not very long after this they embarked on the _Missouri_; and, with the aid of their oars and the current, they proceeded at the rate of between sixty and eighty miles a day. On the 7th of August they reached the mouth of the _Yellow-stone river_, the place of rendezvous, appointed with Captain Clarke. Here, by a note stuck upon a pole, they were informed that he had accomplished his voyage along that river, and would wait for them lower down the Missouri.