Arguments are presented to support the proposition that Ultrahelvetic Flysch basins were present on both sides of the Habkern island arc that was convex to the southeast during Paleocene time. The width of this Ultrahelvetic realm of sedimentation is estimated to have been at least 300 km in a northwest-southeast direction; this estimate is based upon comparison with the geometrical dimensions of modern basins and on paleoecological considerations. The deformational history of the Ultrahelvetic Flysch is interpreted in terms of plate tectonics. Two plates were involved, a Helvetic plate and a Penninic plate. The origin of the Flysch basins was related to the descent of the northward-moving Penninic plate under an island arc which was at the leading edge of the Helvetic plate. During late Eocene and early Oligocene, a plate flip took place and the Helvetic plate then descended below the Penninic plate. This reversal in plate relationships accounts for the occurrence of the discordant Bergell Pluton and concurrent andesitic volcanism, which supplied detritus to the North Helvetic Flysch.