148 Professor W. M. Davis — River Meanders. 



enter the main river meandering freely on a flood plain where its 

 curves turn toward them. 



The simplest conditions under which a tributary should be led 

 to enter its master at an abnormal point are found in the occurrence 

 of a cut-off, as in Fig. 4 ; but this special case would soon be brought 

 under the rule, either by the development of a new meander which 

 will usually grow towards the tributary in the neighbourhood of the . 

 cut-off,^ or by the approach of the next up- valley meander. 



A second group of examples would include rivers that follow 

 relatively narrow meandering valleys, like those of the lower Wye, 

 the lower Seine, the lower Moselle, or the north branch of the 

 Susquehanna. Here the same rule may be expected to apply to the 

 entrance of the tributaries, and that for two reasons. In the first 

 place, because such rivers have, it may be said with much confidence, 

 incised their meandering valleys from a meandering course that they 

 formerly possessed on the upland in which the valleys are incised, 

 when that upland was a lowland of erosion. On such a lowland the 

 rivers must have reached a late stage of their cycle of development, 

 and in a late stage they must have been meandering freely. While 

 the uj)lift was going on and afterwards, the meanders would have 

 been incised beneath the uplifted lowland ; but the entrance of the 

 tributaries has not been thereby significantly altered from whatever 

 orderly arrangement they had gained during the former lowland 

 stage of erosion. 



In the second place, if by chance any abnormally entering 

 tributary existed when uplift and incision began, the normal processes 

 of widening the meander belt and of shifting the meanders down- 

 valley, which must accompany incision, would sooner or later bring 

 about a normal entrance in the same manner as on an alluvial flood 

 plain, shown on Fig. 3, but at a lower rate than there obtains. An 

 excellent instance of this kind is known in the lower Seine, where 

 the Ste. Aiistreberte has been taken in at Duclair, not far below 

 Eouen, precisely as illustrated in Fig. 3. 



Another instance of the same kind occurs on the Marne not far 

 east of Paris (see "The Seine, the Mouse, and the Moselle," Nat. 

 Geogr. Mag., 1896, vii, 191). The Moselle exhibits at least one 

 illusti'ation of the entrance from the south-east of a small tributary, 

 the Veldenzer Bach, on a concave stretch a short distance up-stream 

 from Berncastel ; but this is demonstrably the result of a cut-off, as 

 shown in Fig. 4 (ibid., pi. xxii, opp. p. 193). 



These normal, effective, and fully verified habits of change in the 

 course of a meandering river seem to account very fully for the rule 

 that tributaries usually enter where the river curves toward them ; 

 a rule that Mr. Callaway shows to obtain for various rivers in many 

 parts of the world, and that is supported by certain additional 

 examples that I have recently inspected. 



^ The changes following the occurrence of a cut-off, as illustrated on the maps of 

 the Mississippi, show that the growth of a new meander towards the cut-off and 

 abandoned meander, but a little further down-valley, is not unusual. 



