NE-SAW-JE-WON 



of Cincinnati, but with removal of the ice barrier the river 

 returned to its former course. 



The Records Made by Rivers and Lakes 



Nature today continues to make the same sort of records 

 she has always made on the face of the earth. As the work 

 of living glaciers supplies the key to knowledge of the ancient 

 ice invasions, so does the work of modern streams and lakes 

 furnish the key to the records made by rivers and lakes of 

 the past. Each river and lake writes its own life-story. Start- 

 ing as small rills or brooks, rivers increase in size as they ac- 

 quire tributaries. At the same time they use tools found in 

 their paths or supplied by tributaries — cobbles, pebbles, 

 gravels, and even huge boulders in flood times — to cut and 

 carve their channels deeper. Having deepened their channels 

 to the limit of their power, they wear away their banks. The 

 net result is the production of a valley, narrow near the 

 source of the stream and widening into a broad flaring "V" 

 toward the outlet. The cross-section of the valley is also 

 V-shaped, being a sharp V near the headwaters and almost 

 flat near the mouth. Tributary streams enter with their cur- 

 rents directed downstream, so that in time the river system 

 has the familiar "tree," or dendritic, pattern. The streams in- 

 crease in length by headward cutting (even when the source 

 is in a lake, the lake is drained eventually) and by building 

 deltas at the mouth and then cutting across them. As the 

 river grows old, it will have drained the lakes in its course and 

 built a wide flat on which it swings lazily and muddily from 

 bank to bank, like the Mississippi. By contrast, in the areas 

 which have been glaciated the drainage is poor and hap- 

 hazard, for pre-glacial stream courses have been more or less 

 filled with drift, the streams diverted, and waters ponded to 

 form lakes and swamps. Tributaries may enter the main 

 stream at any angle, valleys may be wider near the headwaters 

 than near the mouth, small streams may occupy much-too- 



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