HUMAN RELICS OF LANSING, KANSAS 753 



its erosion and deposition are intimately conditioned by its rela- 

 tion to the river. In all such cases there is a strong presump- 

 tion that the erosions and depositions at the mouth of such a 

 tributary, such especially as have brought it into adjustment to 

 the present and to the recent stages of the river, were contem- 

 poraneous with those stages and not accidental inheritances. 



5. Meandering as a cause of alternate erosion and deposition. — 

 A meandering river with a deep, readily-shifted, bottom-filling 

 of the Missouri type imposes upon its tributary valleys alternate 

 stages of excavation and filling. These result (1) from the action 

 of the aggressive bends of the river loops against the mouths of 

 the tributaries, and (2), the replacement of these, after a time, 

 by the flood-plain peninsulas that lie within the loops. More 

 specifically, it is the alternate cutting of the stream itself, work- 

 ing hard against and under the mouth of the tributary valley, 

 followed by the building up of the river's higher flood-plain 

 across the mouth of the valley. The first causes the waters of 

 the adjusted tributary to erode; the second to make deposits in 

 the mouth of the tributary; for in the first stage the axis of the 

 tributary opens out on the river itself, which may be twenty or 

 thirty feet, or more, lower than the upper flood-plain, and hence 

 the tributary then has its lowest and best opportunity to discharge 

 its waters and their detrital burden. Besides this, the river itself, 

 while in this aggressive attitude, sweeps into the mouth of the 

 tributary in its flood stages and aids in its excavation, and the 

 rushing by of the river's strong current drags out by friction, on 

 the principle of draught, the waters of the tributary, and, by 

 acceleration, aids their excavating action. It is at this stage pre- 

 eminently that the tributaries cut down their valleys into adjust- 

 ment with the main stream bed. On the other hand, when the 

 active impinging bend of the river has shifted elsewhere, and in 

 its stead a flood-plain is being built up across the mouth of the 

 tributary the drainage of the latter is checked, and if the tribu- 

 tary be small and its waters incompetent in comparison with the 

 flood-plain aggradation of the river, the valley mouth will be 

 filled to a height corresponding to thatof the highest flood-plain. 

 Now, the difference between low water and high water for the 



