Toronto Star: Alexander Mackenzie kept a careful record of his troubles 224 summers ago, scribbling about torments like cold, driving rain and clouds of ravenous mosquitoes as he paddled a bark canoe north to the Arctic. For days on end in early June 1789, he journeyed along the shores of Great Slave Lake, blocked at each turn by ice, searching with native guides for a route to the river that would eventually take his name. Some 600 kilometres south of the Arctic Circle, lake ice was a constantly shifting barricade,...