336 John Casper Branner 



matter, if spread over the hydrographic basin of the Arkansas 

 River above lyittle Rock* — 140,000 square miles — would have 

 a thickness of .000,082 of a foot ; the total dissolved matter 

 would have a thickness of .000,024 of a foot, or the total sus- 

 pended and dissolved matter would be .oco,io6 of a foot in 

 thickness. Erosion over this area during the year 1887-8 

 therefore took place at the rate of one foot in 9433 years. 



The interpolations made in the observations on sediments 

 discharged, necessarily detract from the value of the con- 

 clusions reached in regard to the quantity of material car- 

 ried out of the basin. These conclusions must, therefore, 

 be accepted only with the confidence to which the methods 

 followed in the work entitle them. The means at the com- 

 mand of the Geological Survey did not permit the exhaustive 

 observations that were desirable ; indeed, that a thoroughly 

 satisfactory set of observations should be made with the 

 modest appropriation of a state Geological Survey is quite out 

 of the question. The observations have some value, however, 

 on account of their never having been made at this pointf be- 



of the St. Louis, Iron Mountain, and Southern Railway bridge on the 

 north bank of the river. 



No. 5. — Sp. gr. 1.8090. Collected at the foot of Spring St. on the 

 south bank of the river. A cube of 21.9 grams -^as dried at 120° C, and 

 allowed to stand several days in the air. 



No. 6. — Sp. gr. 1. 17603. Collected Nov. 13, 1888, about 15 feet east of 

 the St. Louis, Iron Mountain and Southern Railway bridge on the 

 south bank of the river. 



Nos. I, 2, 3, 4, and 6 were air dried. 



No. 7.— Sp. gr. 2.5632. A mixture of the sediment from six bottles 

 of water collected for sediment determinations. May 2, 1888. 



The specific gravity of the dissolved matter is assigned it from the 

 specific gravities of the constituents (in their proper proportions) found 

 by analyzing the filtered water. 



* The area of the hydrographic basin above Little Rock was kindly 

 furnished by Henry Gannett of the U. S. Geological Survey. Other 

 estimates make it somewhat larger. 



tThe investigations of Humphreys and Abbot include a series of dis- 

 charge and current measurements on the Arkansas River at Napoleon. 

 As those authors point out, however, (Physics and Hydraulics of the 

 Miss. River, 1876, p. 33) the water of White River was included in their 



