16 IOWA STUDIES IN NATURAL HISTORY 



streams are diverted and beheaded, drainage is reversed in 

 direction, and still other crooks are developed. During any 

 one of these first stages in stream adjustment, streams may 

 reach temporary grade, on the upstream sides of resistant 

 rock or upstream from glacial dams, blocking lava flows, 

 landslides, or artificial dams, and develop meanders. Finally, 

 when the stream has developed its valley to old age, has 

 large tributaries and large volume, and has reached a still 

 later stage of adjustment, the stream is sluggish, is likely 

 to be depositing, is easily turned from side to side, and 

 stream meanders, as the term is commonly applied, are 

 formed. The crooks developed in the first three stages as 

 outlined above, may be formed and intrenched in a single 

 cycle of erosion. It would require an uplift and a second 

 cycle of erosion for the intrenchment of the meanders de- 

 veloped in the fourth stage. If meanders be defined as the 

 curves acquired by a stream in the late stages of valley de- 

 velopment, intrenched meanders would be proof of a second 

 cycle of erosion. But a difficulty lies in distinguishing such 

 meanders from crooks developed during earlier stages. 



The writer does not see any means of distinguishing 

 crooks developed in youth on a flat surface (Fig. 4, AA and 

 BB) nor meanders formed on temporary flood plains up- 

 stream from obstructions, from meanders developed in old 

 age (Fig. 4 DD and EE). It seems even difficult, and in 

 many cases impossible to distinguish the meanders of old 

 age from ordinary crooks due to topography, irregularities 

 of resistance, or stream piracy (Fig. 4 CC). 



It has been said that meanders differ from other crooks, 

 (1) in being more symmetrical, (2) in being so arranged 

 that every portion of the stream course is a part of two 

 meanders, and (3) in having a ratio of distance across the 

 necks of meanders to distance around the meanders of about 

 1 to 7. A study of the courses of the Missouri and Sioux 

 rivers on the Elk Point, S. D. topographic sheet, the Mis- 

 souri and Platte rivers on the Leavenworth, Kas. sheet, Mis- 

 sissippi river on the Baton Rouge, La.. sheet, Missouri river 

 on the Marshall, Mo. sheet, the Wabash, White and Patoka 

 rivers on the Princeton, Ind. sheet, the Wabash and Little 



