STRUCTURE OF THE DRIFT BORDER. 45 



streets. The occurrence of a distinct soil and weathered zone between 

 the loess and the upper or Illinoian till sheet is a feature not noted by 

 McGree; with this exception his description applies well to the exposure. 

 The section, as determined November, 1897, is as follows: 



Section of drift at comer of Sixth and Harrison streets, Davenport, Iowa. 



Feet. 



Iowan loess, partly eroded 8 



Black soil 1 foot, with Illinoian till surface leached and reddened to a depth of 3 feet in the San- 

 gamon interglacial stage; total 4 



Brown calcareous till, with a few calcareous nodules ; traces of horizontal bedding near bottom, 

 but with few vertical fissures or seams, a characteristic Illinoian till 7 



Brown till, calcareous, with numerous vertical fissures and seams, and occasional horizontal 

 sand partings, with tendency to break in cubical blocks, a characteristic oxidized Kansan till . 8-10 



Blue-gray till, calcareous, with occasional horizontal saud partings and numerous vertical seams, 

 also tendeucy to break in cubical blocks; bowlder-like masses of gravelly saud often 2 or 3 

 feet in diameter, in some cases showing crumpling of beds, occur in the lower part of the 

 exposure; a characteristic unoxidized Kansan till; entire depth 35-40 



Fine sand, appearing ouly on Harrison street, at base of exposure 3 



Total, about ■ 70 



The base of this exposure stands about 50 feet above the level of the 

 Mississippi River, while the top of the exposure is nearly at the level of 

 the uplands. In this exposure no leached zone appears at the junction of 

 the Illinoian and Kansan, probably because of removal by the Illinois ice 

 lobe. The change in physical character upon passing from the brown till 

 of the Illinoian to that of the Kansan is very striking. The Illinoian may 

 be denoted a friable or crumbling till, while the Kansan is a caking till 

 where characteristically developed. 



The next exposure examined presented a weathered zone and evidence 

 of erosion* between the Illinoian and Kansan, and also showed the Iowan 

 loess in its full thickness. It is found along Eighth street in a steep descent 

 between Myrtle and Vine, and is as follows: 



Section of drift along Eighth street, between Myrtle and Vine streets, Davenport, Iowa. 



Feet. 

 Iowan loess 



Reddish-brown surface of Illinoian till sheet, leached and stained during Sangamon inter- 

 glacial stage 2* to 3 



Brown calcareous till, crumbling readily; a characteristic Illinoian till 15 



Ash-colored gummy clay with black streaks, apparently of humus, representing the Yarmouth 

 interglacial stage 2 to 3 



Brown till, calcareous, fracturing in cubical blocks, color changing to grayish blue at 12 to 15 

 feet; characteristic Kansan till 25 



Total, about 7;s 



