midnight
They did not , however , reach this portion of their voyage until very late in the evening , when they arrived at the head of that long and gentle bit of water called the Sans Sault Rapids . The river here was about a mile wide , but offered no bad chutes . The captain told them that it only took eight minutes to run through , but that the time coming up with the steamboat usually had averaged one and three-quarter hours . The strange , luminous twilight of the sub-Artic day continued until midnight . It was , indeed , after eleven o'clock when the steamer struck that narrow shut-in of the Mackenzie River where the great flood , compressed between high and rocky shores , runs steadily and deep for a very considerable distance . Above the actual beginning of the narrower channel lay a great , deep pool , many hundreds of yards wide , while at the right hand of its lower extremity sprang up a bald white rock face of limestone . So sharp was the bend of the great river here that at the turn it seemed as though the river itself had come to an end or had dropped out of sight .