366 NATURAL HISTORY BULLETIN. 



pale bluish post-Kansan loess interposed between the gumbo 

 and the yellow loess. In a road-cut in the north-central part 

 of section 21, T. 78 N., R. 6 W., about three feet of yellow 

 loess overlie about six feet of bluish fossiliferous loess. 



In the northeast quarter of section 4, T. 79 N., R. 6 W., 

 a fossiliferous bluish loess lies below a non-fossiliferous yellow 

 loess. 



In a number of exposures southwest from Iowa City the 

 upper loess only is present, and is sometimes fossiliferous. 

 That the lower, bluish loess is pre-Iowan is shown in the ex- 

 posures along the Cedar Rapids and Iowa City Electric rail- 

 way in Jefferson township, Johnson County, Iowa. 



In the first exposure north of the river about seven feet of 

 Kansan drift is exposed at the base; upon this rests an irregular 

 band of Buchanan gravel, over which lies a bed of bluish 

 fossiliferous loess (post-Kansan), twelve feet in thickness, and 

 over this a layer of sand, probably Iowan. In the third cut 

 north of the river* six feet of bluish fossiliferous loess appear 

 at the base; upon this rest four or five feet of sand, in places 

 with pebbles, and evidently Iowan drift, and over this a newer 

 loess about two feet in thickness. The third, fourth, seventh 

 and eighth cuts north of the river, in sections 21, 16 and 17, 

 show pale bluish loess covered by from two to four feet of 

 Iowan drift, largely sand and gravel, over which lies a foot of 

 newer loess. 



With the exception of the Muscatine cut all these exposures 

 are near the Iowan drift border, and show that all the loess of 

 this region is not Iowan or post-Iowan, for the bluish loess is 

 certainly pre-Iowan and shows much greater age. Its bluish 

 materials were probably derived directly from the Kansan 

 blue clays when they formed the old land surfaces. 



At the "Quarry" west of West Amana, Iowa County, Iowa, 

 four feet of Kansan drift rest directly on the carbonifer- 

 ous sandstone; above this are four feet of Iowan drift, and 



*See Plate XII, fig. 2. 



