Patterns of deposition at the continental margin 307 



basins which are so characteristic of the southern section. The continental slope ofT 

 the west Florida platform (Fig. 3) represents the most striking submarine fault 

 scarp known at present, in places attaining a height of over 7000 feet. This can be 

 traced around the Keys into Florida Strait, but its height has diminished to about 

 600 feet (Jordan, 1954). 



HoLTEDAHL (1950) Concluded that the Norwegian shelf consists of consolidated 

 rock which probably belongs to the same complex which makes up the hinterland, 

 that is, granites and metamorphics, and that the whole is partially covered with a 

 veneer of glacial debris of all types. The slope is controlled by what are apparently a 

 series of step faults. Obviously, any comparisons as regards a depositional origin of 

 the slope can no longer be made in this case, and there is nothing now to suggest a 

 sedimentary origin for this entire borderland. Possibly it represents the eroded roots 

 of a former eugeosyncline upon which no " paraliageosynclinc " has been built, 

 for lack of an adequate area from which the sediments might have been supplied. 



A case that appears to be somewhat analogous is found off the end of the Breton 

 Peninsula. Extensive areas of rocky bottom extending out towards the continental 

 slope are shown on the chart of bottom lithology appearing in the Atlas de France 

 for 1935, with Dangeard as the authority. It would be reasonable to suppose that 

 the igneous complex making up this peninsula plunges beneath the sea, although 

 there is no notation of rock types, and there are no charts which give any clear 

 picture of bottom topography. 



There is enough diversity in the examples cited above to make the geologist pause 

 before assigning any blanket mode of formation to the continental shelf and slope. 

 It is not our purpose here to review the older mechanical theories such as the abrasion 

 platform and the marine delta. Today they have few adherents (Dietz, 1952). It is 

 becoming apparent that each continental margin must be studied on its own merits; 

 its history, structure and hthology must be known, and we must also know something 

 about the oceanographic conditions which control sedimentation beyond the coast- 

 line. Without adequate marine topographic surveys we are still only guessing, and 

 these must be supplemented by bottom coring and dredging. The case presented here 

 for offlap and onlap is an attempt to reduce the sedimentary picture to its simplest, 

 most primitive terms, in situations where oceanographic conditions have remamed 

 constant for long periods of time. From this point on it will be obvious to anyone 

 that an endless succession of variables can be introduced to alter the pattern of the 

 prototype. 



REFERENCES 



Daly R A (1936), Origin of submarine " canyons ". Amer. J. Sci., 31 (186), '*0'-420 

 DiTTZ R. S. (1952), olomorphic evolution of continental terrace (contmental shelf and slope). 

 Bull. Amer. Assoc. Petrol. GeoL, 36(9), \m2-\Sl9 .u. n^v «f H,.n>, ,1 Curn-nt Sci 23 



Dietz, R. S. (1954), Possible deep sea turbidity current channels m the Bay of Bengal. Curnnt be. Z^ 



DiExtT's and Menard, H. W. (1951), Origin of abrupt change in slope at continental shelf 



GBA.\^;l'r(r95ffTo1fogra1rhy-o1rion\S Nonhwes. Gulf of Mexico. B.,„ ..-oi 



H^N.-'ra:, EwSo? M:'and ERicsoN, D. B. (1955) Reconnaissance survey of .he aby»al plain 



south of Newfoundland. Deep-Sea Res., 2 (2), 122-133. 



