It is thus by sub-glacial aggradation that the prairies have been leyelled up to a smooth surface, in contrast to the higher and non-glaciated hilly country next south.
Below St Paul), a picturesque expansion of the river across its flood-plain, is due to the aggradation of the valley floor where the Chippewa river, coming from the north-east, brought an overload of fluvio-glacial drift.
Flood plains may be the result of planation, with aggradation, that is, they may be due to a graded river working in meanders from side to side, widening its valley by this process and covering the widened valley with sediment.
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