The Bathurst Island group, and Byam Martin Island, together occupy about 8,000 square miles of land area. They are situated near the geographic center of the Canadian Arctic Archipelago and encompass the north magnetic pole. Most of the area is covered by sedimentary rocks of Ordovician to Late Devonian age, with a composite exposed thickness of approximately 20,000 feet. Exposures of younger rocks are limited to small areas in the northwest and southeast. The oldest rocks exposed are Ordovician evaporites and carbonates; these are overlain by Upper Ordovician to Lower Devonian black graptolitic shale. The black shale sequence is followed by increasingly coarse-grained elastic rocks, including, turbidites, of Early Devonian age. Unconformities and marked facies changes indicate three pulses of Devonian uplift of eastern Bathurst Island. Middle Devonian rocks are mainly carbonates grading basinward to shales. The Upper Devonian is represented by a thick sequence of paralic and nonmarine quartz-rich elastic sedimentary rocks which blanket the whole island group. The next record of sedimentation consists of a few hundred feet of Permian and Mesozoic strata which occur on Cameron and Helena Islands, in the northern part of the area. Upper Cretaceous plant-bearing sandstone and shale with an interbedded basalt flow occurs in a graben in southeastern Bathurst Island; nearby dykes and plugs probably are related to the flows. Two fold belts intersect at near right angles in eastern Bathurst Island. The north-south trending Cornwallis Fold Belt along the east coast first developed in Early Devonian time, and the east-west Parry Islands Fold Belt developed later. The younger belt had its first and main deformation between Late Devonian and Early Permian time in the Ellesmerian orogeny. A third period of deformation affected the entire area during the Late Cretaceous and probably Tertiary time. Included in this episode were faulting, intrusion and further folding of both the Cornwallis and Parry Islands Fold Belts. The Cornwallis Fold Belt largely resulted from differential vertical movement in the underlying Precambrian basement. The Parry Islands Fold Belt is an allochthone that moved southward, above a décollement that apparently is in the Ordovician evaporites. A zone of left lateral strike slip movement in the western part of the Cornwallis Fold Belt delimits the eastern boundary of the allochthone. Western parts of the Cornwallis Fold Belt were involved in the décollement.