Knowledge Bank

North-south-trending and arcuate lobate moraine systems occur in LaSalle County. The till of the arcuate system is characterized and distinguishable by relatively coarse texture, high magnetic susceptibility, carbonate, and zirconium contents, as compared with the north-south moraine system. The arcuate system seems to be particularly influenced by Ordovician and Silurian rocks. Illite is the dominant clay mineral of all tills. Iron-rich chlorite is markedly oxidized in the more permeable tills of the arcuate system.