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Hydrogeologic framework of LaSalle County, Illinois

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. PURPOSE AND OBJECTIVES The investigation described here was undertaken after detailed soil mapping of LaSalle County was completed. In contrast to most of Illinois, the relatively thin veneer of loess overlying till in this area makes it imperative to correctly identify the texture of till when classifying soils. Samples of calcareous till were taken from 1 to 2 ft below soil profiles in calcareous till of the moraines (fig. 1) in an effort to characterize certain of their physical and chemical properties and to determine if the moraines had unique mineralogical characteristics. Winters and Wascher (1935) and Wascher and Winters (1938), in previous studies of till in northeastern Illinois, found great variability in texture and also determined that differences in texture were not coincident with moraine boundaries.

Robert L. Jones

Papers

Mineralogical and Physical Characteristics of Till in Moraines of Lasalle County, Illinois