Only a few areas of the world are sufficiently well sounded to provide data for a study of structural benches. One cannot expect to see identical structural benches in each profile even across a slope composed of a laterally uniform series of horizontal beds of contrasting lithologies. The exact mode of erosion, the local system of jointing, and chance variations in a number of other variables make it necessary to have a large number of closely spaced, accurately located profiles. We are fortunate that the Coast and Geodetic Survey has surveyed virtually the entire continental slope from Georges Bank to Norfolk, Virginia. Almost all these sounding lines are run at right angles to the strike of the topography and are thus suitable for analysis of structural benches. In this same area the dredgings of Stetson (1936) on Georges Bank and the Esso Hatteras Light test provide us with information on the stratigraphy of the sediments which form the continental shelf and slope. The seismic work of Ewing and collaborators (1937 _et seq._) provides us with further information on the dips and on the depths of a number of sedimentary rock series of contrasting lithology. Fishermen began finding fossiliferous rocks on Georges Bank well over a century ago. They were not particularly pleased to obtain rocks instead of fish and generally threw the accursed rocks back into the sea. Some curious fishermen brought a few of the rocks to shore, however, and in time some of these were received by the museums (Upham, 1894; Dahl, 1925). These rocks contain Tertiary and Cretaceous fossils. The depths and positions of recovery of the rocks were generally unknown to the museums, and no clear idea could be gained of the exact occurrence of this material. Stetson (1936; 1949) conducted a series of scientific dredging operations in the Georges Bank area. His aim was to recover more of these older rocks from known depth ranges and positions. He concluded that the older rocks outcrop only in the submarine canyons. He found no consistent depth ranges for the series of Miocene and Upper Cretaceous rocks obtained. [Illustration: FIGURE 20.--_Georges Bank canyons_ Chart shows position of sounding lines and dredge hauls used to construct projected profile and inferred geologic section shown in Figure 21 (a). Sounding lines from Coast and Geodetic Survey Chart 1313.]