recently, the recognition that most of the area of every continental shelf 

 is covered by relict sediments deposited at times of lowered sea level during 

 ice ages. Less vi^ell knovi^n is the internal structure of continental margins. 

 Only about 150 continuous seismic reflection profiles have been published 

 that cross major parts of the continental margins of the world. These 

 few profiles, augmented by gravity and magnetic profiles, and supplemented 

 by analysis of rock dredgings and of projections of features on adjacent 

 land, permit only a general classification of the structure underlying the 

 continental shelves. They do show the presence of buried folds, faults, 

 unconformities, salt domes, and calcareous reefs — all important potential 

 traps for oil and gas. 



Regional studies by oceanographic institutions have discovered much 

 valuable scientific information about the origin and age of continental 

 margins. Most striking, perhaps, is the discovery that the North American 

 continental margin dates from the Early Mesozoic. An ancestral land mass, 

 suggested in Figure 25, split apart at that time. Sea-floor spreading 

 carried North and South America westward, away from Europe and Af- 

 rica. The record of this event may be preserved in the sediments and 

 structures of the continental margin of Africa. 



The continental margin off western Africa, shown in Figure 26, is 

 one of the world's most important. Its length is about 12,000 kilometers, 

 from 35° north to 35° south latitude. A general reconnaissance of the en- 

 tire region should solve many questions about sediment patterns on opposite 



sides of the ocean and of the ancient breakaway of North and South ci 



America from Africa. More important, it might well locate general areas 

 of promise for mineral and non-living resources that are as yet unsuspected. 

 Outstanding examples of this possibility are the discovery and initial 

 exploitation of the hugh oil and gas fields in the North Sea that were 

 completely unknown less than 10 years ago, the presence of petroleum pre- 

 dicted for the Atlantic shelf of the United States and Canada, and those 

 predicted for the East China Sea. In only one of these cases had oil or gas 

 been found in quantity on the adjacent land. 



As part of its participation in the International Decade of Ocean Ex- 

 ploration, the Woods Hole Oceanographic Institution is beginning a study 

 of the African part of the eastern Atlantic continental margin, using ad- 

 vanced equipment for seismic reflection, seismic refraction, geomagnetics, 

 gravity, precision bathymetry, and satellite navigation, aboard the re- 

 search vessel Atlantis II, shown in Figure 27. The geophysical traverses 

 will be rather broadly spaced, about 200 kilometers apart, extending 

 across the continental shelf, slope, and rise, with some of them extending 

 to the Mid-Atlantic Ridge. Total length of all traverses is about 72,000 

 kilometers. 



According to present plans the first cruise (except for steaming to 

 the working area) will start in Capetown, South Africa, in early Febru- 

 ary 1972 and will end at Lagos, Nigeria, in late June, with intervening 

 port stops at Walvis Bay, Southwest Africa ; Lauanda, Angola ; and Libre- 

 ville, Gabon. The second cruise will begin at Lagos in late January 1973 

 and end at Oporto, Portugal, in early June, with intervening port stops at 

 Monrovia, Liberia ; Dakar, Senegal ; and Las Palmas, Canary Islands. 



