Most Earthcaches I've visited offer views of unique rock formations, geysers, or deep vistas. Since I'm a born and bred prairie person I thought it was appropriate to help remind everyone that the prairie is also a geological formation, which took thousands of years to be formed.
The prairie soil here is world reknown for its ability to grow cash crops such as soy bean and corn. I've always thought of it as black dirt, but now know there is a lot of difference in dirt, even here in Macon County. Here's a little background:
Parent material is the unconsolidated material in which a soil forms. It determines the chemical and mineralogical composition of the soil. Most of the parent material in Macon County is a direct result of the glaciers and sediments of the Illinoian and Wisconsinan age. Although the kinds of parent material are associated with glacial deposits, the properties vary greatly, mostly because of varying methods of deposition. The dominant kinds of parent material in Macon County are till, outwash, loess, and alluvium.
These materials were deposited by wind, water, glaciers, and glacial meltwater. In some areas, the materials have been reworked by wind or water after they were deposited. Many of the soils formed in
more than one kind of parent material. For example, many of the soils in Macon County formed in loess and in the underlying outwash or till.
Till is material laid down directly by glaciers. It consists of clay, silt, sand, gravel,and boulders, all of which are mixed together. Unweathered till is generally alkaline, calcareous, and very dense. Through the processes of soil formation, the upper 1 to 2 meters of the till that is exposed to biological activity becomes less alkaline and less dense. Senachwine soils are examples of soils that formed in till.
Outwash is stratified material deposited by flowing glacial meltwaters. The size of the particles that make up outwash varies, depending on the velocity of the moving water. Typically, outwash is dominated by material that is fine sand or coarser. The coarser material was deposited nearer to the ice or in rapidly moving glacial meltwater streams. Most of the outwash deposits were later covered by loess. In
Macon County, coarse outwash material occurs in glacial valley areas now dominated by stream terraces or on small kames or eskers. Stratified, medium textured outwash material was deposited on an outwash plain all along the leading edge of the Shelbyville and Cerro Gordo moraines.
Camden, Starks, and Brooklyn soils are examples of soils that formed in loess and in the underlying stratified outwash on outwash plains. Sparta soils are examples of soils that formed in outwash along
valley trains on outwash terraces. Broadwell soils are on bluffs and outwash terraces above the flood plain along the Sangamon River.
Peoria Silt, or loess, is material deposited by the wind. It consists of uniform silt sized particles that were calcareous before they were acted upon by leaching. The meltwaters from the glaciers carried vast quantities of silt, which were deposited in the major river valleys. As these sediments were exposed when the meltwaters subsided, winds carried these silts and deposited them over much of the land. Most
of the soils in the county formed at least partially in the nutrient-rich loess. The thickness of the loess ranges from virtually zero in areas where slopes are very steep to more than 80 inches. Buckhart, Clarksdale, Ipava, Osco, and Sable soils are examples of soils that formed in more than 80 inches of loess. Birkbeck, Blackberry, Camden, Catlin, Drummer, Flanagan, Milford, Raub, and Wingate soils
are examples of soils that formed in loess over other materials within a depth of 80 inches (fig. 12). Peotone, Shiloh, and Harpster soils formed in mixed loess and colluvial sediments.
The sandy silt facies of the Roxana Silt Formation is material composed of mixed silty and loamy sediment from loess and drift material. It typically lies below Peoria Silt and above the Illinoian till in a soil profile. It is commonly weathered and may show signs of stratification, compaction, paleo-development, rock structure, or mixing with adjacent parent material layers. This parent material is not common in Macon County.
Alluvium is material that was deposited by floodwater from modern streams. Soils that formed in alluvium are generally stratified in both color and texture. The alluvial soils mostly consist of silty sediments, but in some places the soils have thin layers of loamy and sandy material. Ross soils formed in loamy alluvium. Huntsville, Sawmill, Tice, and Wakeland soils are examples of soils that formed in silty sediments. Wabash soils formed in clayey sediment. These soils occur on active flood plains and are relatively younger than many of the other soils in the county. Consequently, these soils have a weakly developed subsoil. The largest areas of alluvial soils are along
the Sangamon River and its tributaries.
(Most of this information came from the 2007 USDA Soil Survey of Macon County.)
Logging requirements:
Send me a message titled “Prairie View” to me with answers to the following questions:
1. How many are in your party?
2. What type of soil do you think is in this area?
3. How deep do you think this soil is?
4. When did the Illinoian and Wisconsinan ages occur?
I hope you enjoyed this Prairie View as much as I do!
