Cores from the subsurface Deadwood Formation contain typical Cordilleran Zone D assemblages of trilobites, brachiopods and gastropods. One core contained Tremadoc and early Arenig graptolites. New taxa are the hystricurid trilobite Galbretina andrewsi n. gen. et. sp., and the graptolite Mastigograptus macrotheca montanensis n. subsp.

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