Geology of Seneca Township

  Back to Land Use Plan

GEOLOGY OF SENECA TOWNSHIP

Seneca Township was formed hundreds of millions of years ago when the geology of the area was primarily igneous and metamorphic rocks. During this same time period the region was covered by water forming shallow inland seas. Many forms of fossil life were formed such as limestone. Over this time a large gradual depression known as a geosyncline formed boundaries from Illinois-Indiana to the western part of Nebraska. The valley formed by this large depression had a depth of 4 to 5 miles.

About 4 million years ago a series of land glaciers came down from central Canada to transform the area we call the Mid-West. Most of the rich soils and rock of Canada were stripped away by these land glaciers and brought to this area. These million year glacial period four successive glaciers moved down to the Mid-West. The last glacial movement was 10,000 years ago. These continental glaciers were 10,000 feet thick. Because of their thickness and weight they acted as a large bulldozer and filled low areas and made the central plains flat. The action of these glaciers created the richest farmland in the world, including significant areas of land in McHenry County and Seneca Township.

The soils in Seneca Township consist of over one hundred different soil types. Of these various soil types there are six major soil groups that make up the majority of the soils found in the township.

  • Group 27 – Miami Series
    The Miami soil group consists of deep well-drained soils formed in loess and the underlying glacial till on uplands. The surface layer is dark brown silt loam about 4 inches thick. The subsoil is dark yellowish brown silty clay loam and clay loam in upper 22 inches, dark brown loam in lower 5 inches. The substratum is brown loam. Slopes range from 0 to 60 percent. This soil is most suitable for use as cropland, pastureland and woodland.
  • Group 79 – Dakota Series
    The Dakota soil group consists of well drained soils formed in loamy deposits and the underlying sandy deposits on glacial out wash plains, stream terraces and valley trains. The surface soil is very dark brown and very dark grayish brown loam about 14 inches thick. The subsoil is dark yellowish brown and brown loam in the upper 12 inches, brown sandy loam in the next 4 inches and brown loamy sand in the lower 5 inches. The substratum is dark yellowish brown sand. Slopes range from 0 to 18 percent. This soil group is most suitable for use as cropland.
  • Group 149 – Brenton Series
    The Brenton soil group consists of somewhat poorly drained soils formed in loess or silty sediments and in the underlying loamy out wash in out wash plains and terraces. The surface layer is black and very dark gray silt loam that is 16 inches thick. The subsoil is brown and dark yellowish brown silty clay loam that is 37 inches thick. The substratum is mixed brownish yellow and light gray stratified silt loam. Slopes range from 0 to 43 percent. This soil group is most suitable for use as cropland.
  • Group 219 – Millbrook Series
    The Millbrook soil group consists of somewhat poorly drained soils formed in silty over loamy sediments on out wash plains, terraces, and fans. The surface layer is very dark grayish brown silt loam about 7 inches thick. The subsurface layer is dark grayish brown silt loam that is 7 inches thick. The mottled subsoil is yellowish brown and gray silty clay loam in the upper 30 inches and gray and yellowish brown stratified clay loam and sandy loam in the lower 11 inches. The substratum is stratifies sandy loam and loam. Slopes range from 0 to 5 percent. This soil is most suitable for use as cropland.
  • Group 224 – Strawn Series
    The Strawn soil group consists of soils that are well drained formed in glacial till or uplands. The surface layer is dark grayish brown silt loam that is 4 inches thick. The subsoil is brown and dark brown loam and clay loam that is 15 inches thick. The substratum is yellowish brown loam. Slopes range from 2 to 60 percent. This soil is most suitable for use as cropland.
  • Group 265 – Lomax Series
    The Lomax soil group consists of well drained soils formed in alluvial and out was materials on terraces and uplands. The subsoil is dark brown sandy loam in the upper 11 inches and strong brown stratified sand and sandy loam in the lower 9 inches. The substratum is yellowish brown sand. Slopes range from 0 to 5 percent. This soil is most suitable for use as cropland.
    • As can be seen from the above listing of soil groups and their properties, the majority of the soils located in Seneca Township are well suited to agricultural production.