Erosion in the Basin of the Arkansas River 329 



river at all stages, but especially during high water, and which 

 adds enormously to the amount of material daily and hourly 

 carried out of the hydrographic basin of the Arkansas River 

 above Little Rock.* 



Character of the Sediments.— Tue matter in mechanical sus- 

 pension in the river water is both sand and clay. Samples 

 taken from the thread of the stream are mainly of fine sand, 

 but samples of sediments allowed to settle in the quiet eddies 

 of the river show that the lighter and more flocculent sedi- 

 ments sink to the bottom only in the quiet portions of the 

 water. 



An analysis was made of the sediments collected in six 

 samples of river water of the i ith of April, 1888, two each from 

 top, middle, and bottom of the stream. 



ARKANSAS RIVER SEDIMENT FROM THE STREAM. f 



Sand and insoluble matter, 85.18 per cent. 



Soluble matter, 14.82 " 



The soluble portion contained : 



Iron oxide, (Fe^O ), . . . "j 



Alumina, (Al.Oj), .....'.*.'.' .' ." / 4-96 



per cent. 



On this occasion the river was very high, standing at 17 

 feet on the gage, but it had been higher by half a foot two 

 days before. 



A complete analysis was made of the sediment collected 

 with six litres of water May 2d, 1888, when the river stood at 

 17 feet on the gage after a sudden rise, and while the rise was 

 still in progress. It is as follows : 



* In the Annual Report of the Chief of Engineers, U. S. A., 1875, II, 

 p. 478, Col. J. H. Simpson shows how sand-bars travel down-stream. 

 See also Physics and Hydraulics of the Miss. River, by Humphreys and 

 Abbot, 1876, p. 147. 



t Analysis by Assistant Dr. Jas. Perrin Smith. 



