Erosion in the Basin of the Arkansas River 327 



weighed. The amount of matter in solution was determined 

 by evaporating the filtered water. These determinations were 

 made for every sample collected during the year— 358 deter- 

 minations.* A daily record was also kept of the stage of the 

 river during the time covered by the investigation. 



These observations furnish data for the approximate deter- 

 mination of the discharge of the Arkansas River, and of the 

 amount of material carried by it, both in suspension and solu- 

 tion, past Little Rock, during the year in which the observa- 

 tions were made (1887-8). 



Suspended Matter. — The color of the water of the Arkansas 

 River is due to mineral matter carried in mechanical suspen- 

 sion. It is more or less muddy all the year round, and even 

 at its lowest stages, when it carries least sediment, it is not 

 quite clear. Its color is ordinarily a yellowish brown, but it 

 sometimes becomes dark red, at which times it carries such a 

 large amount of mechanical sediments as to render it opaque, 

 even as seen in an ordinary test tube. 



The laws of erosion and transportation naturally lead one 

 to expect a large amount of mechanical sediments to be re- 

 moved when the volume of water or discharge is greatest. If 

 the conditions which supply sediments to the stream were 

 constant, this would undoubtedly be true, but the conditions are 

 not constant, and the amount of material moved depends upon 

 the .sediment-supplying conditions rather than upon the trans- 

 porting power of the water. 



The matter in suspension is greatest during a sudden high 

 rise ; but after the water in the stream stands at any high 

 mark for a few days, the decrease of the amount of suspended 

 matter it carries is very marked. This contrast is most no- 

 ticeable during the winter, probably because the frosts loosen 

 up the surface soil and leave it in a condition favorable for 

 ready transportation. The amount of sediment carried by the 

 river varies widely also with the same gage reading at any 

 stage, being greater with a rising, and less with a falling 

 river. 



* The laboratory determinations were made under my personal direc- 

 tion by Dr. R. N. Brackett. All the care required by quantitative 

 chemical analyses was taken with this work. 



