38 



The National Geographic Magazine 



to the Gulf. The same opening out of 

 meanders is noticed at Teesmouth and 

 at the mouth of Seine and Dniester. 

 The Panaro and Tagliamento come 

 from their mountains overburdened with 

 waste, and flow where it encumbers 

 them in braided courses. The mean- 

 dering stretch examined for each comes 

 just below. 



The facts ascertained by an exami- 

 nation of incised rivers are of suffi- 

 cient interest to be now summarized 

 in Table B. 



The ratios run high. The average 

 is 30.6. Of all single rivers studied, 



The Forth at Stirling 



the most interesting is the Dniester, 

 with two measurements in each table. 

 On the flood plain its ratios are 14.3 

 and 1 6 A, and 34 and 36 where incised 

 in the mountains. This is the same 

 story as the longer tables tell of mean- 

 der belts that widen out as they are 

 incised in the rocks. It is to be noted 

 that the river widens in the mountains, 

 but the meander belt widens even more. 

 The exceptionally high ratios for 

 Seine, Oise, and Marne go with the 

 quite as exceptional symmetrical form. 

 The Seine and Marne at least are quite 

 as regular in their curvature as the 

 Mississippi and quite of the flood-plain 



type. Note the large ratio — . One 



might look for some local cause for all 

 three did not the Agout, in the south- 

 west of France, agree with them. Yet 

 farther from Paris, Seine 24 and Seine 

 26 have values nearer normal. Is there 

 interference with the streams by wall- 

 ing or dredging sufficient to explain 

 this abnormal ratio ? The great use of 

 these streams for interior commerce 

 might easily lead to a deepening of the 

 channels at important points, and this 

 would tend to narrow the stream and 

 increase the meander ratio. The width 

 tabulated for Seine 25 is suspiciously 

 small. This would be comparable to 

 what has happened to the Rhine 

 at Mannheim in the process of 

 "correcting" that stream. 

 Seine 25 and 26 have their chan- 

 nels divided in two by a contin- 

 uous line of islands, as in the 

 Rhine in the Schiefergebirge, but 

 more numerous. Very likely the 

 Agout has too great a width as- 

 signed to its meander belt because 

 of what I may call compounding 

 of meanders, which very often 

 makes it hard to measure flood- 

 plain streams, notably the Koros 

 on the plain of Hungarj-. The 

 accompanying sketch of the Forth 

 at Stirling illustrates this com- 

 pounding. Cd may be regarded 

 as the immediate axis and A B as the 

 original axis. Such forms are common 

 in the small tributaries along the central 

 valley of the Mississippi. 



In contrast to the curves of the Seine 

 just noted are the stiff zigzags of the 

 Nolichucky and French Broad shown on 

 figure 5, as characteristic of inherited 

 incised meanders. We must think of 

 them as once swinging freely on a low- 

 lying plain, but their incision in the 

 rising land has set them rushing swiftly 

 from turn to turn where once they 

 swung in curves. The deep-cut mean- 

 ders of the canyons of the Colorado ap- 

 pear from the maps to have nothing of 

 stiffness or zigzag in their form. 



