THE SEINE, THE MEUSE, AND THE MOSELLE 
197 
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 valle}" 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 geograph}^ 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 Geographical Journal 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 Penns^dvania and northern 
New Jersey. * 
In the general discussion of this problem we should recognize 
two divisions. First, the processes by Avhich 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 
^larne near Chalons, than whicli no better example lias come to 
my notice an3'where in the world. 
The case of the Marne below Chalons. — In the province of Cliam- 
jiagne the Marne drains an extended interior lowland inclosed 
liy a forested upland on the west. The lowland is the ]>roduct 
of comparatively rapid erosion during late Tertiary time on weak 
upper Cretaceous strata. It is for the most jiart covered b}^ ex- 
tensive farms. The uiiland stands where the lower Tertiarv 
strata have, during the same period of time, more successfully 
resisted erosion. As the dip of the strata is gentl}' westward, the 
eastern margin of the upland is marked by a steep escarpment. 
The .Marne gathers man,y branches from the lowland, and escapes 
on its way to the sea li}' a deep vallc}' cut through the upland. 
♦Tkk Natio.val Gkoohaphic Maoa/.ink, Wiisliingtoii, i, 188f); ii, 1800. 
