X-ray diffraction data indicate that profiles developed on Wisconsin, Illinoian, and Kansan tills in Indiana differ from each other with respect to the stages attained in clay-mineral alteration. The post-Wisconsin weathering profile is distinctly different from the buried profiles on Illinoian and Kansan tills, but the differences are not quite so great between the weathering profiles developed during the Sangamon age on Illinoian tills and those of Yarmouth age on Kansan tills.

Hydration and ionic exchanges produce major changes in clay-mineral alteration, but oxidation, hydrolysis, polymerization, and recrystallization also play significant roles. The final alteration products of clay minerals are determined by the composition of the original clay and the duration of alteration.

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