Note 128 — Chapter VIII · THE RIVER-ROUTES

In studying the variations of the bed of the Paraná it is necessary to avoid comparing maps drawn at dates separated by long intervals. The differences of such maps are such that they do not enable us to follow the processes by which the actual forms have been derived from earlier forms. The analogies which they show are sometimes due, not to the permanence of the topography, but to the return of a complete cycle of changes, or of conditions analogous to the earlier conditions.