Enroute to Tampa last week, my flight made a stop in Louisville, Kentucky. As we descended across the forested hills of southern Indiana, I was delighted by the autumn colors and amazed by the large number of quarries that dot the landscape. This is, of course, limestone country.
Traveling east to west across the southern half of the Hoosier State, one encounters bedrock that gradually decreases in age. The southeast corner of Indiana sits atop Ordovician shales and limestones; further to the north and west, these give way to Silurian dolomites and then a band of Devonian sediments. In south-central Indiana, Mississippian limestones dominate the scene, including the famous Salem Limestone (commonly referred to as Indiana Limestone); deposited in a shallow sea, 340 million years ago, this exceptionally pure and workable stone has been used to construct many of America's landmark buildings, including the Empire State Building. Forming a jagged swath from northwest of Bloomington to southeast of Bedford, the Salem limestone is up to 60 feet thick. Further west, Pennsylvanian sandstones, harboring seams of coal, stretch into southern Illinois.
Living as we do on the outermost, thin veneer of Planet Earth, we tend to ignore the layers of history that lie beneath our feet. Miners and geologists know better!
