Abstract In the western part of the Arctic Archipelago of Canada two structural provinces are dominant. They are the Ellesmerian Orogenic Province and the Sverdrup Basin. The Ellesmerian Orogenic Province extends in a great arc from northeastern Ellesmere Island to eastern Prince Patrick Island. That part of it that lies on Bathurst and Melville islands, west of the Cornwallis Fold Belt, includes the Parry Islands Fold Belt, which is typified by the structures of Bathurst and Central Melville islands. The western sector of the Sverdrup basin lies north of the Parry Islands Fold Belt. Its axis strikes southwest and its southern erosional margin is the northern limit of exposure of the Parry Islands folds. The illustrations that follow show typical Parry Islands fold structures, and a major diapiric structure of the Sverdrup Basin. The Parry Islands fold belt has a known length of about 565 to 600 km (350 to 375 mi). Its width as seen on Bathurst Island is about 175 km (120 mi), and on central Melville Island is about 150 km (90 mi). The full width is not known because its northern margin is hidden beneath the rocks of the Sverdrup Basin; it probably does not extend far beneath the basin. The known stratigraphic succession ranges in age from Early Ordovician to Late Devonian (Figure 2). It is believed that there are also Cambrian and Proterozoic sedimentary rocks, but nothing is known of their sedimentary facies or thicknesses. In southern Melville Island the Paleozoic and Proterozoic sedimentary section appears to be at least 10,000 m (33,000 ft) thick, as concluded from seismic reflection data. The Cambrian through Late Devonian beds are the southern basinal rocks of the Franklinian Miogeosyncline. These fall readily into two megasequences — the Lower Ordovician to Middle Devonian consists of units of limestone, dolomite, shale, halite, and anhydrite, and the late Middle through Upper Devonian sequence consists of a great thickness (as much as 4,500 m; 14,750 ft) of shale, siltstone, and sandstone. The response of these beds, primarily by folding, to southerly directed orogenic pressure produced the Parry Islands Fold Belt. Two parts of the succession played a vital role in determining the style and intensity of folding from place to place. The Bay Fiord salt served as a decollement zone, a mobile substratum, above which folding proceeded. In areas where there is no Bay Fiord salt the Ellesmerian Orogeny produced structures very different from the typical Parry Islands folds. An important role also was played by the Late Ordovician to Middle Devonian facies. In areas where that interval comprises limestone and dolomite of the Blue Fiord, Read Bay, and Allen Bay formations, the orogeny produced broad, relatively short, rather unsystematic folds. Where the interval comprises the Eids and Cape Phillips shales, with the Bay Fiord salt at depth, the folds erected are the typical Parry Islands type.