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106 through the Great Slave River and the Mackenzie, into the Arctic Ocean. From the headwaters of Peace River Mackenzie passed on west to the stream which later took the name of Fraser River, and after following the river for some distance, struck directly west for the Pacific, which he reached in July, 1793. Mackenzie was the first man who crossed the continent to the Pacific Ocean north of the Spanish possessions, which at that time had an indeterminate northern boundary. This boundary was fixed afterward at the forty-second parallel by treaty between the United States and Spain.

On the results of the expedition of Mackenzie and of the voyage of Vancouver the British Government was already basing a large and general claim to sovereignty on the Pacific. President Jefferson hastened the organization of the exploring expedition to go overland from the United States, for the purpose of strengthening the rights we had acquired through Gray's discovery, and of anticipating further expeditions and claims of Great Britain. Lewis and Clark were not here too soon, for the English already had other expeditions in preparation, and their explorers were on the Upper Columbia but a little later than the return of Lewis and Clark from the mouth of the stream. Simon Fraser, in 1806-8, followed to the sea the river that bears his name, believing at first, as Mackenzie before him had believed, that he was on the Columbia; and another Englishman, David Thompson, whose name is perpetuated in the well-known tributary of the Fraser, was the first man who explored the upper courses of the Columbia River, and some years later he followed it through its whole course to the sea—arriving at Astoria in July, 1811—some four months after the occupation by the Americans. President Jefferson had been exceedingly anxious that the Lewis and Clark expedition should escape the notice of Great Britain and of the British Northwest Company, with whom disputes about territorial rights were feared—but in fact, the expedition did not escape their notice; for no sooner did Lewis and Clark appear on the Missouri than their expedition was