The computer-derived contours and color ramp shown on this map show the shape of the bedrock surface in Bartholomew County. The shaded relief on the map shows the modern topography. The bedrock surface is the surface that marks the top of lithified rock. In Bartholomew County, and throughout Indiana, the bedrock surface is the erosional top of Paleozoic sedimentary rocks. Typically covered by soils or much younger (Quaternary or Tertiary) deposits of unconsolidated sediment, it is locally visible at natural outcrops of bedrock or in man-made excavations that penetrate bedrock. The position of the bedrock surface is economically important because it marks the abrupt transition from easily excavated unconsolidated sediments into solid bedrock and because it limits the lateral and vertical extent of economically important bedrock units.