The Precambrian basement in Indiana (SG-06)
Only about 20 drill holes in Indiana have reached these rocks. From these holes and from seismic soundings geologists have gotten a glimpse of the geologic history representing most of the time that has elapsed since the earth was formed. And they have learned that the Basement is only about 3,000 feet below the surface in east-central Indiana, more than 2 miles deep in southwestern Indiana.
Samples of granite, basalt, and marble from the deep holes differ greatly from the sedimentary bedrock on which we live and from which we get most of our mineral resources. Knowledge of these rocks is important because similar rocks elsewhere contain rich mineral deposits. And their position in some places in Indiana controls the structure of overlying rocks that may contain gas and oil.
Our Hoosier State Beneath Us: Structural Geology