Abstract The Cow Head Breccia in western Newfoundland is a slope sequence within a Taconic klippe transported from the southeast. The Cow Head Breccia accumulated on the western side of the proto-Atlantic ocean from the Middle Cambrian through early Middle Ordovician. The 310 m sequence consists of limestone breccia and thin beds of lime mudstone, calcarenite, green silty shale, marl, and radiolarian-sponge spicule chert. Paleotopo- graphic maps for the Cambrian and ordovician parts of the Cow Head Breccia show that a stable paleoslope configuration existed for 70 million years. As the 10 by 75 km klippe is oriented, the regional paleocontours of the paleotopography trend northwest-southeast with a paleoslope that dips northeast. The spectacular megabreccias contain algal-rich, oolitic, fossiliferous limestone boulders that reach 60 by 150 m in size. These breccias were deposited by gravity-controlled viscous mass flows that travelled downslope from narrow carbonate platforms that trended northwest-southeast near Cow Head and Martin Point. Bottom currents consistently flowed southeast, parallel to the paleocontours. The southeast-flowing contour currents deposited mostly nongraded beds of calcarenite, but also some graded beds in the Upper Cambrian. U-tube trace fossils of Arenicolites are oriented parallel to the contour currents. As the proto-Atlantic narrowed during the Middle Ordovician, the continental margin rapidly subsided leading to deposition of 200 m of red shale, followed by more than 400 m of volcanogenic sandstone and gray shale. Within the basin, the northeast-dipping paleoslope shifted to dip northwest. During the Taconic Orogeny the klippe was transported to the northwest by gravity sliding within the basin.