The Kugururok formation, of Late Devonian age, consists largely of dolomite and limestone with minor shale, sandstone, and conglomerate, and is probably more than 2,000 ft. thick. The Mississippian Lisburne group is divided into 3 marine formations: the Utukok, Kogruk, and Tupik. The Utukok formation is at least 2,500 ft. thick at its type locality and consists mostly of ferruginous sandy limestone, calcareous and quartzitic sandstone, and calcareous shale. The Kogruk formation, as much as 1,500 ft. thick, is composed of thick-bedded, fine- to coarse-grained, gray limestone with minor beds and lenses of chert. The Tupik formation, as much as 700 ft. thick, is predominantly dark gray to black, finely crystalline limestone and black chert. Geographic distribution of these units is shown, and they are compared with the Devonian and Mississippian sequence in the Shainin Lake area, central Brooks Range. Other unnamed Devonian and Mississippian units in and near the De Long Mountains area are briefly described.