National Geographic : 1896 Jun
THE SEINE, THE MEUSE, AND THE MOSELLE fine illustration of the significant features of river interaction in this region. A remarkable case of river diversion occurs in the shift of the course of the Vistula from its former path down the valley now occupied by the Netze to a more northward course, by which it flows directly to the Baltic sea, the point of change being at the town of Bromberg. This is well illustrated on the Prussian topo graphical maps, and has been described in a general way by various writers on the geography of North Germany. Whether it was caused by the spontaneous interaction of streams com peting for drainage area or not, I shall not at this distance ven ture to say, but shall hope to find a full explanation of the change in a forthcoming essay by Berendt. Jukes-Brown has described an interesting case in England, where the Trent cap tured the headwaters of the Wytham, and in a recent volume of the GeographicalJournal of London I have attempted a more general treatment of the same region. Readers who wish to fol low the subject into examples of greater intricacy may find some problematic examples in the rivers of Pennsylvania and northern New Jersey. * In the general discussion of this problem we should recognize two divisions. First, the processes by which it is accounted for, these having just been summarily described. Second, the topo graphical forms by which its occurrence may be recognized, dis tinction being made between examples occurring in the remote or the recent past and others likely to occur in the near or dis tant future. Illustration of the second division of the subject can best be given by describing the concrete case of the river Marne near ChAlons, than which no better example has come to my notice anywhere in the world. The case of the Marne below Chdlons.-In the province of Cham pagne the Marne drains an extended interior lowland inclosed by a forested upland on the west. The lowland is the product of comparatively rapid erosion during late Tertiary time on weak upper Cretaceous strata. It is for the most part covered by ex tensive farms. The upland stands where the lower Tertiary strata have, during the same period of time, more successfully resisted erosion. As the dip of the strata is gently westward, the eastern margin of the upland is marked by a steep escarpment. The Marne gathers many branches from the lowland, and escapes on its way to the sea by a deep valley cut through the upland. * THE NATIONAL GEOGRAPHIC MAGAZINE, Washington, i, 1889; ii, 1890.