Collection part of scattered localities, statigraphic position determined by field-mapping correlations (from faunal list given on Table 2, pp. 8-9 in Campbell, 1967)

Fossil locality shown on Plate 1

The name Kogruk(?) Formation is applied to thick dolomitic section (unit Ml₄ of Campbell 1960a, b) in the Lisburne Group of this area because its stratigraphic position is similar to that of the Kogruk Formation as described by Sable and Dutro (1961, p. 592) in its type area in the western DeLong Mountains (from Campbell, 1967, p. 14)

Fossil material consists of abundant crinoid columnals and undetermined echinoderm debris and subordinate Bryozoa, horn corals, small colonial corals (including lithostrotionoid corals, particularly near the base), brachiopods of several species, and at least one blastoid (table 2). The fossil collections were examined by J.T. Dutro, Jr., and Helen M. Duncan, of the Geological Survey, who report (written commun., 1961) that the fossils appear to correlate with those in the upper part of the Alapah Limestone of the central Brooks Range. Several collections represent a Chester-type assemblage of bryozoans, brachiopods, and echinoderms. Dutro and Duncan also note that the collections correlate broadly with the Gigantoproductus zone of the central Brooks Range and that Gigantoproductus has been found in similar rocks near Cape Lisburne. They further suggest (written commun., 1961) that the Kogruk(?) Formation and most of the underlying Nasorak Formation are faunally equivalent to the type Kogruk of the western DeLong Mountains. The presence of Late Mississippian fossils in the Kogruk(?) and in the upper part of the underlying Nasorak Formation suggest that all the rocks assigned to the Kogruk(?) in this area are of Late Mississippian age, whereas the type Kogruk Formation of the western DeLong Mountains is considered to be of Early and Late Mississippian age (Sable and Dutro, 1961, p. 592). (from Campbell, 1967, p. 18)

Collection 58ACr36 contains two poorly brachiopods, Linoproductus? sp. and a large indeterminate spiriferoid, of types not ordinarily found in the Utukok formation in the Brooks Range. A Late Mississippian age is suggested for this collection as well.

Both collections consist of a rock type common in the Alapah limestone, in various places, and separately mapped as the Tupik formation (name not yet published) in the DeLong Mtns.