6 FIELD OPERATIONS OF THE BUREAU OF SOILS, 1918. 



Great Sand Mound is undulating, while the remainder of the first 

 bottom, with the exception of a small area in the vicinity of Hope- 

 well School, which is undulating, is level. 



The lowlands along the Iowa River vary from 2 to (> miles in width, 

 the maximum being reached in T. 76 N., R. 5 W. Another large 

 expansion occurs in the vicinity of Wapello. These lowlands consist 

 of first-bottom land, subject to overflow, and second bottoms or 

 terraces, lying entirely above the highest floods. The first bottom, 

 with the exception of the two lobelike extensions in T. 76 N., R. 5 W., 

 caused by former meanderings of the river, occurs as a strip ranging 

 from three-fourths mile to 2 miles in width, intersected by many 

 sloughs and old ox-bow lakes. The terrace occurs in three main areas, 

 namely, west of Cedar River and north of the Iowa River; northeast 

 and southeast of Fredonia; and northwest, west, south, and southeast 

 of Wapello to a point beyond Elrick. The terraces are traversed in 

 places by the valleys of streams issuing from the uplands. In the 

 extreme northwestern part of the county, on the east side of the Iowa 

 River, both first bottom and terrace contain numerous knolls and 

 ridges, and in places the line of separation as drawn between first 

 bottom and terrace is of necessity rather arbitrary. In other places, 

 particularly east and northeast of Fredonia and south and south- 

 west of Wapello, a ridge occurs near the margin of the bluff and this 

 also makes the boundary between terrace and upland somewhat 

 indefinite. Elsewhere, with the exception of a few slight ridges and 

 knolls on the terrace, both ten-ace and first bottom are nearly level. 

 For the most part the terrace rises abruptly about 20 feet from the 

 bottom, but the narrow strips of terrace occurring within the first 

 bottom are only 8 to 15 feet above the latter, and rise from it in a 

 rather gentle slope. 



The eastern upland area or drift plain is a southern extension ol 

 the Illinoian drift plain in Muscatine County.^ On the northern 

 county boundary it is about 9 miles wide, but it gradually tapers to 

 a width of about 2 miles northeast of Wapello, whence a tongue 

 projects about 8 miles farther southeast. The plain has an average 

 elevation of about 100 feet above the lowlands. It is moderately 

 dissected, the topography varying from level to broken. Tlie more 

 broken areas occur on the steep slopes leading to the Iviississippi 

 River bottoms. In general the topography is gently rolling. The 

 general slope is toward the west, with the exception of the north- 

 eastern part of Grand view Township, which slopes toward the east. 

 The east bluff rises very abruptly to an elevation of 100 to 150 feet 

 above the lowland and is broken only by two small creeks which 

 flow out across the Mississippi bottoms, one leaving the upland one- 

 half mile south of the north county line and the other about 6 miles 



I See Geology of Louisa County, by J. A. Udden, Iowa Geol. Survey, Vol. XI, 1900, p. 62. 



