1883, John Macoun, Manitoba and the Great North-West, Thomas C. Jack, pages 60–61Among the hills are basin-like valleys, round, or irregular in form, and without outlet, which are sometimes dry but generally hold swamps or small lakes, which have frequently been filled in with material washed from the hills so as to become flatbottomed.
1973, Richard G. Wilkinson, Poverty and Progress, Methuen & Co Ltd, ISBN 0-416-08660-8, page 159:The great width of the rivers allowed the development of flatbottomed boats capable of carrying hundreds of tons of cargo.
