Date: Cretaceous Period (145-65 million years old)
Description: Limestone is a sedimentary rock that is largely composed of calcite crystals. Calcite, or calcium carbonate, is formed by calcium-rich sediments mixing with the remnants of dead marine animals: bits of shells, bone, etc. Limestone deposits are great places to find fossilized sea life, but for Sioux City it is far more important as a building material. Marble, terra-cotta, and limestone clay for bricks were key materials that made masons, quarrymen, and manufacturers thrive in Sioux City. Limestone in this area is often covers by thick layers of loess and nutrient-rich silt from ancient floods.
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