In North Greenland, the crystalline basement is unconformably overlain by a late Precambrian to early Paleozoic sedimentary sequence. The Inuiteq So Formation, containing conspicuous basic intrusions, is at least 1,000 m.y. old; the youngest dated strata are Middle to Late Silurian. A southern platform sequence of unmetamorphosed homoclinal strata passes northward into the east-west-trending North Greenland fold belt, in which mainly Cambrian to Silurian rocks are exposed. In western North Greenland, the upper part of the platform section is a reef complex showing facies changes between reef carbonate rocks and offreef argillaceous rocks.

In eastern Peary Land, folded lower Paleozoic beds underlie a cover of less severely deformed Pennsylvanian, Permian, Triassic, and Cretaceous-Tertiary strata which show the effects of Tertiary deformation. In northern Peary Land, the folded metasedimentary units have been transported northward over the Kap Washington Group of bedded lavas and tuffs along the Kap Cannon thrust. These volcanic rocks have given a minimum K-Ar age of 35 m.y.

In Peary Land, where the widest section of the fold belt is exposed, five tectonic-metamorphic zones are recognized; the deformational and metamorphic effects increase northward. The metasedimentary rocks have been subjected to a complex late Phanerozoic-Paleozoic tectonic and metamorphic history. Paleozoic orogenesis (Late Silurian to Late Devonian) involved polyphase deformation which produced three essentially coaxial fold phases. Rocks affected by these three phases of folding are overturned northward toward the highest grade rocks, which in northern Peary Land contain amphibolitefacies assemblages. Cretaceous K-Ar ages of the metamorphic rocks suggest a subsequent thermal event of regional importance. Tertiary orogenesis is indicated by evidence of folding, thrusting, and regiona faulting, and of mylonitization and low-grade metamorphism associated with the Kap Cannon thrust.