The late Pennsylvanian (Virgilian) and early Permian (Wolfcampian) parts of the Naco Group include the upper 300 ft of the Horquilla Limestone and the Earp Formation, which is 2700 ft thick. The varied fusulinid faunas of this succession can be divided into 5 assemblage zones which contain the following new species: Schwagerina dunnensis, n. sp., S. silverensis, n. sp., Pseudoschwagerina portalensis, n. sp., and Waerigella chiricahuensis, n. sp. The lowest zone studied is characterized by Triticites cullomensis, and occurs in early Virgilian strata disconformably overlying middle Des Moinesian beds. This early Virgilian sequence is overlain by a zone of middle to late Virgilian fusulinids, Triticites ventricosus sacramentoensis and Triticites cf. T. plummeri, that occurs in the uppermost beds of the Horquilla Limestone and ranges into the lower 20 to 235 ft of the Earp Formation. From the fusulinid distribution and the transitional lithologies it appears that the top of the Horquilla Limestone and the base of the Earp intertongue laterally. The succeeding 540 ft of the Earp Formation contain a fusulinid assemblage of Triticites and Schwagerina characteristic of the Bursum Formation of New Mexico, the Admire Group of Kansas, and Pueblo Formation of N.-central Texas. Of particular interest is the nearly complete transition from Triticites into Schwagerina in the lower part of the Earp Formation. Overlying these beds are 1200 ft of limestone and shale having a Pseudoschwagerina and Triticites assemblage closely similar to that from the Neal Ranch Formation (early Wolfcampian) of the Glass Mountains, Texas. The succeeding 300 ft of limestone beneath the red shale and cross-bedded sandstone at the top of the Earp Formation have Pseudoschwagerina and advanced species of Schwagerina that are similar to the fusulinid fauna from the Lenox Hills Formation (late Wolfcampian), Glass Mountains, Texas. From the Empire Mountains the Concha Limestone has Parafusulina empirensis, n. sp., which, based on its stage of evolution, is probably of Leonardian age.

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