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An attempt is made to clarify the subdivision of the upper Ordovician strata in northwestern Alabama by the use of Bryozoa and associated fauna. The upper Ordovician limestone exposed in northwestern Alabama (and extending into the northeastern Mississippi subsurface) contains abundant fossils, mainly Bryozoa. These may be used to subdivide this section and to correlate the subdivisions with named units recognized in Tennessee.
The upper part of the "Chickamauga" limestone a catch-all term, may be divided into the Leipers and Fernvale formations on the basis of diagnostic bryozoan species. The Leipers formation is recognized by the diagnostic species Monticulipora molesta Nicholson and the absence of Richmond species. The Fernvale formation is charaterized by the presence of six species that are restricted to that formation out of twenty-four species identified. The writer recommends that the use of the name "Chickamauga" be avoided in favor of the more specific Leipers and Fernvale formations.
The geographic area of study has been restricted to Limestone County, Alabama, which lies within a section of the Black Warrior Basin.
Measured sections of six outcrops are presented as a columnar section. A description of the Fernvale and Leipers formations of northwestern Alabama is given with a list of Bryozoa species identified at each collecting locality.
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