164 



THE ILLINOIS GLACIAL LOBE. 



Several chemical analyses of the loess have been made which repre- 

 sent its structure at widely different points. The first four analyses in the 

 table below were made by R. B. Riggs, of the U. S. Geological Survey, in 

 connection with Chamberlin and Salisbury's study of the loess bordering 

 the Driftless Area, and were published in their paper in the Sixth Annual 

 Report of this Survey. No. 1 was taken from the summit of a ridge in the 

 suburbs of Dubuque, Iowa, at a point about 300 feet above the Mississippi 

 River. No. 2 represents a 7-foot stratum of loess lying over brown residu- 

 ary clay near Galena, Illinois, at about 350 feet above the Mississippi River. 

 No. 3, from Kansas City, Missouri, was chosen as a representative of the 

 most pronounced loessial characters at that locality. No. 4 was taken from 

 near the center of Vicksburg, Mississippi, about 200 feet above the Missis- 

 sippi River, and probably fairly represents the upper half of the stratum 

 there, but not the lower portion, which seemed heterogeneous. The remain- 

 ing two analyses were made by Prof. W. A. Noyes for Dr. J. T. Scovell, 

 and are published in the Twenty-first Annual Report of the Indiana Geo- 

 logical Survey. They are designed to illustrate the constitution of the 

 white clay east of the Wabash River, near Terre Haute, Indiana. No. 5 

 represents the subsoil, the sample being from a depth of about 22 inches. 

 No. 6 represents a sample from a depth of only 10 inches. The samples 

 analyzed by Mr. Riggs were dried at 100° C; those analyzed by Professor 



Noyes at 135°. 



Table of analyses of loess. 



SiO..... 

 A1 ; 0,... 

 Fe ; : , .. 

 FeO.... 

 TiO. . . . 

 P 2 O s .... 

 MnO ... 

 CaO.... 

 MgO... 

 Na .0 . . . 

 K,0.._. 

 H 2 (a) 

 CO,.... 

 S0 3 .... 

 C 



