Studies of Jurassic ammonites and Inoceramus from the northeast shore of Puale Bay and from the south side of Alinchak Bay demonstrate the presence of at least 1,500 ft (457 m) of beds of early to middle Bajocian (Middle Jurassic) age. These form the upper part of a sequence that is 1,900 ft (580 m) thick and that consists mostly of dark-gray siltstone except for one unit of coarse conglomerate in its upper part. The siltstone also contains middle to late Toarcian (Early Jurassic) ammonites about 30 ft (9 m) above its base and lies with sharp contact on massive tufaceous conglomeratic sandstone of early Sinemurian age. The upper contact with the Shelikof Formation of Callovian age is marked by an upward change from nonvolcanic gray siltstone that weathers gray to siltston that bears thin beds of white to yellow volcanic ash and consequently weathers brown. The entire siltstone sequence is assigned to the Kialagvik Formation because it is similar lithologically and occupies the same stratigraphic position below the Shelikof Formation.