son. SURVEY OF LOUISA COUNTY, IOWA. 19 



SOILS. ^ 



Oil tho basis of origin and processes of accumulation of the soil 

 material, the soils of Louisa County may be divided into three j)rincipai 

 groups, namely, loessial, glacial, and alluvial. 



Loess, which is the parent material of the most extensive soils, 

 forms a mantle over the glacial drift of the entire upland except 

 where it has been removed by erosion. It is thickest over the eastern 

 part of the upland, being about 20 feet thick along the l)lufrs of 

 the Mississij)pi River and thinning out toward the west. In i)laces 

 south of Elrick and along the west bluff of Iowa River it is 15 feet 

 thick, but a mile west of these bluffs it thins down to 8 feet and con- 

 tmues toward the west at that thickness or a little less. The loess is 

 usually thicker along the slopes of the larger valleys. When the 

 bluffs face the west, the edge of the upland is frequently bordered by 

 a ridge of fine sand. A good example of this is seen north of Wai)ello, 

 northwest and southeast of Hog Back. 



The loess in its unweathered condition is an even-grained material 

 composed largely of silt. The color ranges from light grayish brown 

 to yellowish brown. The material is slightly coherent where undis- 

 turbed, but breaks down readily into a loose, floury dust. Under 

 erosion it has a tendency to mamtain vertical banks, and these often 

 show a columnar structure. A number of distinct soils have been 

 derived from the loess in this area. Differences in their color and 

 composition are due in part to \'ariations hi the original material, 

 but i^robably to a greater extent to tho different conditions under 

 which weatheruig has taken place and to the unequal periods of time 

 during which the processes of weatheruig have oi)erated. The most 

 noticeable changes that have taken place are the accumulation of 

 organic matter in the surface soil, the concentration of clay in the 



subsoil, and the leaching and partial removal of lime from the weath- 



_^ _ 



5 The southwestern part of Louisa County, joins the northeastern corner of Henry County. Small 

 areas in Henry County wore mapped as Marion silt loam but in LouisaCounty the adjoining areas were 

 mapped as Clinton silt loam. The only difference between the two soils consists in the lighter color of the 

 Marion. In the more recent mapping of Louisa County these areas were not considered light enough in 

 color for inclusion in the Marion series. 



In several places along the boundary between the two counties the Grundy soils in Henry County abut 

 against Tama soils in LouisaCounty. This is due to the creation of the Tama series since the Henry County 

 map was completed. The Tama soils differ from the Cirundy in having more penetrable and lighter tex- 

 tured subsoils. 



Wlien Muscatine County was mapped a large part of the area known as Muscatine Island was mapped 

 as low terrace, on the ground that it was thought to lie above possible overflows. When Louisa County 

 was surveyed several years later it was learned that during stages of extreme high water the area overflows, 

 and so the same soil was mapped as an alluvial bottom-land type rather than a terrace type. On the Mus- 

 catine map they are shown as Buckner soils and on Hie Louisa map as Cass, the difference being that the 

 Buckncr soils occur on terraces above overflow and the Cass soils at a lower level and subject to at least 

 occasional flooding. The more detailed work done in Louisa County shows the presence of a loam where 

 it was mapped as sand in Muscatine County. 



