Examination of the silt and clay fractions of two northern Wisconsin soils, Omega loamy sand of the Brown Podzolic group and Ahmeek loam of the Brown Forest group, revealed considerable quantities of interstratified layer silicates. The two soils contained montmorin, vermiculite, chlorite, and illite both as discrete and interstratified components. Regularly alternating montmorin-illite structures, which registered a 28 Å first order diffraction peak, and vermiculite-illite structures, which yielded a 24 Å first order peak, were observed in the fine silt fractions of the Ahmeek loam A3 and B22 horizons, respectively. Weak diffraction peaks in general and lack of binary mixture average spacings was suggestive of ternary or quarternary interstratification of illite, chlorite, vermiculite, and montmorin in the medium and fine clay fractions of the Ahmeek loam horizons. Randomly interstratified vermiculite-chlorite and vermiculite-montmorin, as revealed by comparative basal diffraction peaks before and after heating potassium saturated samples, were evidenced in the fine silt and clay fractions of the Omega profile.

Mixed layer components in the Omega and Ahmeek soils originated from illite and chlorite in the? horizons with a progressive increase in proportions of first vermiculite and finally montmorin with proximity to the soil surface. The observed weathering transitions within the mixed layer structures illustrates the effects of accelerated leaching which has taken place in these coarse textured soil profiles, even though these soils are relatively young (late Pleistocene).