Variation in the pebble composition of Wisconsin glacial outwash sediments in the Wabash Valley has been significantly controlled by the influx of rock fragments supplied by the local Paleozoic bedrock. Dolostone, the dominant rock type, and limestone were derived from the Silurian and Devonian formations that crop out in northern Indiana. Limestone was also furnished by the Mississippian formations that are exposed in central and S.-central Indiana. Clastics were supplied by the Pennsylvanian formations that crop out in the lower Wabash Valley. Chert was contributed by one or more formations in each of the Paleozoic systems exposed in the Wabash Valley. The igneous and metamorphic rocks, whose ultimate source was the Canadian Shield, were supplied by the gravel fraction of Wisconsin till deposits. This study provides an illustrative example of the concept of progressive dilution.