The limonite ores of Shelby, Alabama, which have been mined intermittently since 1846, occur as small grains and pebbles overlying a white sandy-clay zone, and as large masses or "dornicks" underlying the clay zone; all of which constitutes a blanket between the underlying Newala limestone of lower Ordovician age and overlying- thrust mass of Talladega phyllite and slate of probable Precambrian age. The Talladega contains an abundance of small quartz veins, many of which carry pyrite. The Newala limestone locally is an extremely massive, fine-grained or "vaughanitic" high-calcium limestone, without conspicuous jointing or other fractures. Overthrusting of the Talladega locally on the dense Newala and regional uplifts in the Mesozoic and Cenozoic provided the setting for the leaching of the iron from the pyritiferous Talladega and its deposition and retention as limonite on the underlying, impervious Newala limestone.

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