The Kosciusko Formation takes its name from the town that sits on it. The geologist C. W. Cooke proposed the name in 1925 for ledges of sugary to quartzitic sandstone exposed around Kosciusko, the seat of Attala County, replacing the name Decatur sand, which had already been claimed for another formation. South of town, near milepost 158 of the Natchez Trace Parkway, the formation caps the hills just west of the road, above the Winona and Zilpha beds and the flat floor of the Yockanookany valley. It is mostly sand, gray when fresh and weathering reddish orange, with beds of silt, clay and lignite.
It thickens away from Alabama. The federal geologic names lexicon records about 85 feet at the Alabama line and as much as 400 feet in Attala, Holmes and Carroll Counties, and the 2006 quadrangle map estimates 300 feet around Kosciusko, of which only the lower 80 or so are exposed. It is the Sparta aquifer. A 1963 state study found perennial springs and streams numerous on its outcrop, with springs common where its sand rests on clay, and the water soft and low in dissolved minerals but acidic enough to dissolve iron from pipe.
Near its base the sand is locally cemented into very hard quartzite, in layers up to five feet thick that weather out as boulders on hilltops and slopes. The grains are locked together by overgrowths of quartz, and the state's geologists say the stone can sometimes be told from chert only under a microscope. Where the quartzite roofs soft silt, runoff has washed out small caves beneath it. One described in 1963, west of State Highway 43 north of town, ran about twenty feet into a hillside, with a sinkhole 25 by 35 feet nearby.
Getting there
33.0088, -89.6033
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