DRAINAGE.
All the drainage water escapes by way of the Montreal river, whose two chief tributaries are the East and West branches, the latter being considerably the larger. The East branch is without feeders of important size, but the West branch receives a large creek, the Wapus, from the south, and a considerable volume of water enters through Duncan lake.
In common with most rivers traversing the pre-Cambrian region, this water system is marked by a volume of dormant water enormously greater than that being transported at any given moment. With few exceptions the many small tributary brooks rise in lakes or groups of lakes surprisingly large in size, compared with the volume of the out-flowing streams; Otto and Lehmann lakes are drained by a rather sluggish rivulet 8 feet wide and 6สบ deep, although their combined area is about two square miles. The larger streams themselves are only successions of irregular lake expansions which empty from one to another by short, river-like portions containing rapids and falls. The descent is therefore accomplished by a succession of abrupt steps rather than an evenly graded slope. This juvenile condition is directly ascribable to the geological character of the country; soil deposits are insignificant in quantity, leaving exposed a resistant and uneven rock floor in which the streams are unable to carve channels for themselves. Failing to do so they select the readiest egress by filling up impervious rock basins and spilling over at the lowest points into lower ones. In consequence of the scantiness of soils and frequency of natural settling basins, the waters of the whole system are free from suspended matter, and hence lack of an effective graving instrument. Exceptions to this general character occur in the extensive sand plain to the north and west of Duncan lake, where the several small creeks that traverse it are of ordinary fluvial form and gradation, and the waters of which transport large quantities of sand to Duncan lake.