ABSTRACT: Limestones of the Blue River Group (Mississippian age) exposed along the eastern part of the Illinois Basin are the most important source for crushed stone material in southern Indiana. These rocks are thin where exposed in Montgomery and Putnam Counties but thicken in a southerly direction to more than 500 feet in Crawford and Harrison Counties. The Blue River Group includes, in descending order, the Paoli, the Ste. Genevieve, and the St. Louis Limestones. Both the Paoli and Ste. Genevieve contain limestones with the chemical and physical properties necessary for premium crushed stone aggregate, but because the limestones of the St. Louis contain appreciable amounts of chert, silt, and clay in many places, they generally make inferior aggregate. Some high-calcium limestones of the Paoli and Ste. Genevieve are thick enough to be quarried for flux stone, cement raw materials, and other special purposes. Chemical analyses of more than 2,000 samples and physical tests of more than 300 samples give an indication of the quality of Blue River rocks at different locations and provide information to assist in exploring for new quarry sites.