PAPERS ON GEOLOGY 101 



DISTRIBUTION OF THE LOESS 



The loess covered area in the Mississippi Valley is chiefly 

 confined to the surface of the older (Kansan and Illinoian) 

 drift sheets and the driftless area, and is mostly included be- 

 tween the Missouri and the Wabash rivers, occurring in its 

 typical characters but a few miles west of the Missouri, and 

 extending- east of the Wabash in the vicinity of the Ohio 

 river for several miles east of Cincinnati. South of the Ohio 

 river the loess is chiefly limited to a rather narrow belt ad- 

 jacent to the Mississippi, nearly to its mouth. 



Within this general area the distribution of the loess pre- 

 sents the following significant peculiarities : 



1. Except where local topographic features have modified 

 the normal deposition, it is thickest, most typical and most 

 generally fossiliferous on the bluffs bordering the east side 

 of the larger stream valleys, as along the Missouri, Mississippi 

 Illinois, Wabash and smaller rivers, the thickness generally 

 decreasing with increasing distance from the streams. This 

 peculiarity has been noted by all of the students of the loess. 



Leverett 1 says that the general thickness of the loess on the 

 east side of the Mississippi Valley from the driftless area 

 southward the entire length of Illinois, is much greater than 

 on the west side in Iowa and Missouri ; probably twice as 

 great ; and a similar difference exists on the east and west 

 sides of the Valley of the Wabash river. 



Shimek 2 says that the bluffs of the Missouri river from 

 Sioux City to Kansas City, and those bordering the Mississippi 

 are higher, with thicker loess deposits on the east side than on 

 the west. 



In his report on the St. Louis Quadrangle, Fenneman 3 says 

 that the loess is thickest on the east bluffs of the Mississippi 

 and Missouri rivers where in some places it reaches 50 feet, 

 but it thins to only 10 or 15 feet at a distance of only a few 

 miles. 



In many places along the rivers of Illinois as opposite 

 Burlington and below Alton along the Mississippi, the loess 

 has accumulated on the east bluff in dune-like ridges that stand 

 25 to 50 feet above the uplands farther east, and appear as 

 billowy ridges fringing the east banks of the streams. 



1. Frank Leverett: The Illinois Glacial Lobe. Mon. XXXVIII U. S. Geol. 

 Survey, 1899, p. 183. 



2. B. Shimek : Loess Papers. Bui. from the Laboratories of Nat. Hist, of the 

 State of Iowa, Vol. V, No. 4, p. 371. Nov. 1904. 



3. N. M. Fenneman: Geo. and Mineral Resources of the St. Louis Quadrangle. 

 Bui. No. 438, U. S. Geol. Survey, 1911, p. 33. 



