Presents the 'Orogenic hypothesis" to explain the origin of submarine canyons. A sinking ocean bottom tended to draw the edge of the continental shelf downward until relieved by faults parallel to the margin. These permitted the edge of the shelf to slip upwards again until it was even above sea level, reversing the drainage, which was then towards the interior of the continent. Coastal drainage to the sea was re-established with the cutting of canyons. Further sagging of the ocean floor dragged the margin of the continent under water again, canyons and all. Marine abrasion has modified the shelf to its present condition.