Taken in connection with Hearne's journey, this expedition was of great importance as establishing the fact of an Arctic sea of wide extent to the north of the continent. It seemed probable, also, that this sea formed its continuous boundary. But the greater expedition of this intrepid fur-trader was yet to be undertaken. His object this time was to ascend the Peace River, which rises in the Rocky Mountains, and crossing these to penetrate to that unknown stream which he had sought in vain during his former journey. This river, he conjectured, must communicate with the ocean; and finding it, he must be borne along to the Pacific. [Sidenote: Mackenzie sets out for the Pacific.] The explorer set out, accordingly, from Fort Chippewyan on the 10th of October, 1792, pushing on to the remotest trading post, where he spent the winter in a traffic for furs with the Beaver and Rocky Indians. When he had despatched six canoes to Chippewyan with the cargo he had collected, he engaged hunters and interpreters, built a huge canoe and set out for the Pacific. This canoe, it may be mentioned, was twenty-five feet long within, exclusive of the curves of stem and stern, twenty-six inches hold and four feet nine inches beam. At the same time it was so light that two men could carry it three or four miles, if necessity arose, without stopping to rest. In such a slender craft they not only stowed away their provisions, presents, arms, ammunition and baggage to the weight of three thousand pounds, but found room for Mackenzie, seven white companions and two Indians. Up to the 21st of May the party encountered a series of such difficulties and hardships that all save the leader himself were disheartened at the prospect. The river being broken by frequent cascades and dangerous rapids, it was very often necessary to carry the canoe and baggage until the voyage could be resumed in safety; and on their nearer approach to the Rocky Mountains the stream, hemmed in between stupendous rocks, presented a continuance of fearful torrents and huge cataracts. The party began to murmur audibly; and, at last, progress came to a standstill. In truth, there was some reason for this irresolution; further progress by water was impossible and they could only advance over a mountain whose sides were broken by sharp, jagged rocks and thickly covered with wood. Mackenzie despatched a reconnoitring party, with orders to ascend the mountain and proceed in a straight course from its summit, keeping the line of the river until they could ascertain if it was practicable to resume navigation.