Stratigraphy, structure, and graptolites of an Ordovician and Silurian sequence in the Terra Cotta Mountains, Alaska Range, Alaska

The geology and graptolite faunas of the Terra Cotta Mountains in south-central Alaska are described. Three new formations of Paleozoic age are named and described; they include graptolitiferous argillaceous rocks, sandstones, and limestones of the Dillinger Terrane. The structure and tectonics of the mapped area arc also discussed. Ninety-five species of Ordovician and Silurian graptolites, including four new species, are described and illustrated. The faunal succession is divided into nine Ordovician and ten Silurian biostratigraphic zones and is correlated with graptolite faunas found elsewhere.