of W.long.) to the Ungava Peninsula, which abuts on Labrador.

Where this vast region slopes to the Arctic Ocean and Hudson's Bay it is rather low and flat, except between Alaska and the Mackenzie River, and between the Mackenzie and the watershed of Hudson's Bay.

The principal river system in the far North-West is that of the great Mackenzie River, which flows into the Arctic Ocean (Beaufort Sea) through an immense delta, and is one of the longest rivers in the world.

The southernmost sources of the Mackenzie (such as the Peace River and the Athabaska River) rise in the Rocky Mountains to the east of British Columbia.
These waters are stored for a time in Lake Athabaska, and then under the name of Slave River flow northwards into the Great Slave Lake, and out of this, under the name of Mackenzie River, into Beaufort Sea, through an immense delta.

The Great Bear Lake is also a feeder of the Mackenzie.
Two other Arctic rivers at one time thought to be of great importance as means of communication with the Arctic Ocean, are the Great Fish River, which flows into Elliot Bay, and the Coppermine River, which enters Coronation Gulf.