A thick sequence of highly deformed flyschlike metasandstone, slate, and argillite crops out in southern Alaska in the Kenai-Chugach Mountains and on Kodiak and the Shumagin Islands to the southwest. These poorly fossiliferous rocks have long been considered Cretaceous in age because of scattered occurrences of fragmentary shells of Inoceramus. Mainly on the basis of new fossil collections, the age of some of these rocks can now be firmly established as Late Cretaceous (Maestrichtian); the critical fossil is Inoceramus kusiroensis Nagao and Matsumoto. Inoceramus kusiroensis also occurs in the much more fossiliferous and only slightly deformed Matanuska Formation that forms a parallel belt north of the Chugach Mountains. On the basis of faunal, lithologic, and bedding characteristics, the Matanuska Formation is the shelf equivalent of the deepwater, trench, or continental-rise deposits of the Kenai-Chugach Mountains and islands to the southwest. "Inoceramya concentrica" Ulrich occurs with Inoceramus kusiroensis and is Maestrichtian in age, not Early Jurassic as E. 0. Ulrich suggested
in 1910. The syntypes of I. concentrica are refigured and a lectotype is designated.
